Stress measurement device for strengthened glass, stress measurement method for strengthened glass, strengthened glass

Abstract

Provided is a stress measurement device for strengthened glass, a stress measurement method for strengthened glass, and strengthened glass, which can improve the measurement accuracy of the stress distribution near the surface of the strengthened glass. The stress measurement device for strengthened glass includes a light source, a light supply member, a light extraction member, a light conversion member, a photographing element, and a position measurement unit. The photographing element simultaneously or separately photographs two bright line columns, two bright lines, and / or two boundary lines generated by the plurality of different wavelengths of light while maintaining the mutual positional relationship of the strengthened glass, the light extraction member, the light conversion member, and the photographing element. The stress of the strengthened glass in the depth direction from the surface is calculated based on the positions of the two bright line columns, the positions of the two bright lines, and / or the positions of the two boundary lines in the plurality of different wavelengths of light measured by the position measurement unit.

Description

Technical Field

[0001] This invention relates to a stress measuring device for tempered glass, a stress measuring method for tempered glass, and tempered glass itself. Background Technology

[0002] In electronic devices such as mobile phones and smartphones, glass is widely used for the display and main casing. With the increasing thinning and lightweighting of electronic devices in recent years, the glass used in these devices also requires thinner sheets. However, if the glass sheet becomes thinner, its strength decreases. Therefore, to improve the strength of the glass, chemically strengthened glass is typically used. This involves forming an ion-exchange-based surface layer (ion exchange layer) on the glass surface and generating compressive stress to increase its strength. Optical methods are then used to measure the surface stress value to confirm that the glass has been properly strengthened before it is shipped to the market.

[0003] As a technique for measuring the stress of the surface layer of tempered glass, one example is a technique that, when the refractive index of the surface layer of the tempered glass is higher than that of the interior, utilizes optical waveguide effects and photoelastic effects to non-destructively measure the compressive stress of the surface layer (hereinafter referred to as non-destructive measurement technique). In this non-destructive measurement technique, monochromatic light is incident on the surface layer of the tempered glass, and multiple modes are generated through the optical waveguide effect. The light trajectory determined by each mode is extracted, and the image is formed by a convex lens to create a bright line corresponding to each mode. It should be noted that there are bright lines formed by the number of modes.

[0004] Furthermore, in this non-destructive measurement technique, the light extracted from the surface layer is configured such that bright lines of two light components, one horizontal and one vertical, can be observed with the vibration direction of the light relative to the exit surface. Moreover, utilizing the property that the light of mode 1, with the lowest frequency, passes through the side of the surface layer closest to the surface, the refractive index of each light component is calculated based on the position of the bright lines corresponding to mode 1. The stress near the surface of the reinforced glass is then determined based on the difference between these two refractive indices and the photoelastic constant of the glass (for example, see Patent Document 1).

[0005] On the other hand, based on the principle of the aforementioned non-destructive measurement technique, a method is proposed to extrapolate the stress on the outermost surface of the glass (hereinafter referred to as the surface stress value) according to the position of the bright lines corresponding to Mode 1 and Mode 2, and to determine the depth of the compressive stress layer based on the total number of bright lines, assuming that the refractive index distribution of the surface layer changes linearly (for example, see Patent Document 2 and Non-Patent Document 1).

[0006] Furthermore, based on the surface stress value and compressive stress layer depth measured using the aforementioned surface waveguide light measurement technique, a method for defining the tensile stress CT inside the glass and managing the strength of the strengthened glass using the CT value is proposed (for example, see Patent Document 3). In this method, the tensile stress CT is calculated using "CT=(CS×DOL) / (t×1000-2×DOL)" (Equation 0). Here, CS is the surface stress value (MPa), DOL is the depth of the compressive stress layer (unit: μm) generated by exchanging sodium ions for potassium, and t is the plate thickness (unit: mm).

[0007] Normally, if no external force is applied, the total stress is 0. Therefore, tensile stress is generated approximately evenly in a way that balances the value of the integral of the stress formed by chemical strengthening along the depth direction in the un-chemically strengthened central portion.

[0008] However, chemically strengthened glass has also become more diverse due to its increased strength and improved performance, making it impossible to fully evaluate using traditional stress measurement methods.

[0009] For example, there are tempered glasses that have undergone stress distribution control by exchanging lithium-containing glass with potassium and sodium ions, and chemically strengthened glasses that have undergone ion exchange with transparent crystallized glass.

[0010] In chemically strengthened lithium-containing glasses, conventional optical stress measuring devices can evaluate the stress layer near the surface where lithium and sodium are exchanged for potassium, but cannot evaluate the internal stress layer where lithium is exchanged for sodium. Therefore, the compressive stress does not reach zero at the depth DOL of the compressive stress layer where potassium is ion-exchanged, and the depth DOC (in μm) where the compressive stress reaches zero cannot be measured using stress measuring devices utilizing surface waveguide light.

[0011] A method has also been proposed that measures the stress distribution on the glass surface side of the glass depth (DOL_TP) at a location where the stress distribution is significantly greater than that caused by the influence of the two stress layers, and predicts the stress distribution on the glass depth side beyond DOL_TP based on the measurement results (measurement image) of the stress distribution on the glass surface side (for example, see Patent Document 4). However, in this method, since the stress distribution on the glass depth side beyond DOL_TP is not measured, there is a problem of poor measurement reproducibility.

[0012] In crystallized glass, especially for use in displays where transparency is required, the crystallized glass used here has crystal grains much smaller than the wavelength of visible light, making it transparent in the visible field of view. Therefore, using conventional optical stress measuring devices, the stress on the surface formed through the chemical strengthening process can be measured.

[0013] Therefore, in order to maintain the quality of diverse chemically strengthened glasses, it is necessary to measure and manage the distribution of stress down to the depths and the crystallization state in the crystallized glass.

[0014] In recent years, lithium aluminum silicate glass has attracted attention as a type of glass that is easy to ion exchange and can achieve high surface stress and deep stress layer in a short time during chemical strengthening processes.

[0015] The glass was chemically strengthened by immersing it in a high-temperature molten salt mixture of sodium nitrate and potassium nitrate. Both sodium and potassium ions exchange with lithium ions in the glass due to their high concentration in the molten salt; however, sodium ions readily diffuse into the glass, so the lithium ions in the glass exchange with the sodium ions in the molten salt first.

[0016] Here, the refractive index of the glass decreases when sodium ions exchange with lithium ions, and increases when potassium ions exchange with either lithium or sodium ions. That is, the potassium ion concentration is higher in the ion-exchanged region near the glass surface compared to the unexchanged portion, and the sodium ion concentration increases as the ion-exchanged region deepens. Therefore, the refractive index of ion-exchanged glass decreases with depth near its outermost surface, but increases with depth from a certain depth towards the unexchanged region.

[0017] Therefore, in the aforementioned stress measurement device utilizing surface waveguide light, the stress distribution in deeper areas cannot be determined solely by the stress value or distribution at the outermost surface. Consequently, the depth of the stress layer, the CT value, and the overall stress distribution cannot be known. As a result, it is impossible to develop methods for identifying suitable chemical strengthening conditions, and it is also impossible to conduct quality control in manufacturing.

[0018] Furthermore, when aluminosilicate glass or soda glass undergoes chemical strengthening after air-cooling strengthening, the stress distribution or stress value of the chemically strengthened portion can be measured using the aforementioned stress measurement device utilizing surface waveguide light. However, the refractive index change of the portion that is not chemically strengthened but only air-cooled is small, and the aforementioned stress measurement device utilizing surface waveguide light cannot measure it. As a result, the depth of the stress layer, the CT value, and the overall stress distribution cannot be determined. Consequently, it is impossible to develop methods to find suitable chemical strengthening conditions, and it is also impossible to conduct quality control in manufacturing.

[0019] To address the aforementioned issues, a stress measuring device has been proposed that utilizes the scattered light from a laser beam to determine the stress distribution in tempered glass (see, for example, Patent Document 5). This allows for the measurement of the stress distribution in the tempered glass from the surface to its depth, regardless of the refractive index distribution along the depth direction. The stress measuring device includes: a polarization phase difference variable member that alters the phase difference of the laser beam's polarization relative to the laser beam's wavelength by more than one wavelength; and an imaging element that captures multiple images at predetermined time intervals of the scattered light emitted by the laser beam with altered polarization phase difference as it is incident on the tempered glass. Furthermore, by using these multiple images to measure the periodic brightness changes of the scattered light, the phase change of the brightness change is calculated, and based on the phase change, the stress distribution in the depth direction from the surface of the tempered glass can be calculated.

[0020] Existing technical documents

[0021] Patent documents

[0022] Patent Document 1: Japanese Patent Application Publication No. 53-136886

[0023] Patent Document 2: Japanese Patent Application Publication No. 2016-142600

[0024] Patent Document 3: Japanese Patent Publication No. 2011-530470

[0025] Patent Document 4: US Patent Publication 2016 / 0356760

[0026] Patent Document 5: International Publication No. 2018 / 056121

[0027] Non-patent literature

[0028] Non-patent document 1: Yogyo Kyokai Shi (Journal of the Ceramic Industry Association) 87{3}1979 Summary of the Invention

[0029] Invention Summary

[0030] The problem that the invention aims to solve

[0031] In recent years, cover glass used in foldable smartphones has been, for example, with a thickness of 50 μm or less. While tempered glass is used for such thin glass, the depth of chemical strengthening is typically less than 10 μm. In principle, the thinner the glass sheet, the less likely it is to achieve a deeper chemical strengthening depth. Furthermore, in lithium-containing aluminosilicate glass, which is widely used as tempered glass, chemical strengthening using sodium to replace lithium tends to result in a deeper replacement depth, thus increasing tensile energy. Therefore, when chemical strengthening is performed after sodium-lithium replacement or simultaneously with sodium and potassium strengthening, although the surface compressive stress increases, the chemically strengthened surface layer, which has a high potassium ion concentration to suppress tensile energy, tends to become shallower. Moreover, in the chemical strengthening of crystallized glass, because the original crystallized glass is strong, the focus is often on surface damage mitigation measures, and chemical strengthening is often performed only on the outermost surface to suppress tensile energy. Thus, there is a tendency to suppress tensile energy by making the replacement depth of sodium and potassium-based chemical strengthening shallower.

[0032] When measuring the stress distribution of shallowly chemically strengthened glass using a stress measuring device employing waveguide light, the number of bright lines produced is very small; depending on the situation, some glass may only produce one bright line (Mode 1 described later). Shortening the wavelength of the waveguide light source is an effective method to increase the number of bright lines, but when the wavelength is shorter than 350 nm, the transmittance of most optical and strengthened glass decreases, rendering the optical system of the measuring device inoperable or unable to observe the waveguide light. Therefore, there is a limit to methods for increasing the number of bright lines. Consequently, the stress distribution near the surface of very shallowly chemically strengthened glass cannot be accurately measured and quality control is impossible, thus preventing the production of such products.

[0033] The present invention was made in view of the above points, and its object is to provide a stress measuring device for tempered glass that can improve the accuracy of measuring the stress distribution near the surface of tempered glass.

[0034] Solution for solving the problem

[0035] This stress measuring device for tempered glass includes: a light source capable of emitting light of multiple different wavelengths; a light supply member that directs light from the light source into the surface layer of the tempered glass having a compressive stress layer; a light extraction member that directs the light propagating within the surface layer outward from the tempered glass; a light conversion member that converts two light components, which vibrate parallel and perpendicular to the boundary surface between the tempered glass and the light extraction member, into two bright line sequences, two bright lines, and / or two boundary lines generated by the critical angle of the refractive index difference between the tempered glass and the light supply member; an imaging element that captures the two bright line sequences, the two bright lines, and / or the two boundary lines; and a position measurement device. The unit measures the positions of the two bright line columns, the two bright lines, and / or the two boundary lines from the images generated by the multiple different wavelengths of light obtained by the imaging element. While maintaining the relative positional relationships between the tempered glass, the light extraction member, the light conversion member, and the imaging element, the imaging element simultaneously or separately captures the two bright line columns, the two bright lines, and / or the two boundary lines generated by the multiple different wavelengths of light. Based on the positions of the two bright line columns, the two bright lines, and / or the two boundary lines in the multiple different wavelengths of light measured by the position measurement unit, the stress of the tempered glass in the depth direction from the surface is calculated.

[0036] Invention Effects

[0037] According to the disclosed technology, a stress measuring device for tempered glass can be provided that can improve the accuracy of measuring the stress distribution near the surface of tempered glass. Attached Figure Description

[0038] Figure 1 This is a diagram illustrating the stress measuring device of the first embodiment.

[0039] Figure 2 This is a diagram showing the effect when an achromatic lens is used.

[0040] Figure 3 This is a diagram illustrating the pattern.

[0041] Figure 4 This is a diagram illustrating the refractive index distribution of the surface layer of tempered glass.

[0042] Figure 5 It is a diagram illustrating the ray trajectories of each mode when multiple modes exist.

[0043] Figure 6 This is a diagram illustrating the columns of highlighted lines corresponding to multiple patterns.

[0044] Figure 7 This is a diagram illustrating an example of the trajectory of light from a light source between the tempered glass and the prism.

[0045] Figure 8 It is an example of a bright line array with two wavelengths (1).

[0046] Figure 9 This is an example of a bright line arrangement captured by a camera element.

[0047] Figure 10 It is a diagram illustrating the movement of the imaging element.

[0048] Figure 11 It is an example of a bright line array with two wavelengths (the second one).

[0049] Figure 12 It refers to the diagram where the bright lines overlap (Figure 1).

[0050] Figure 13 It refers to the diagram where the bright lines overlap (Figure 2).

[0051] Figure 14 This is a diagram illustrating the trajectory of light inside the glass.

[0052] Figure 15 It is a graph showing the image and brightness curves of two types of bright lines.

[0053] Figure 16 It is a standard reinforced glass bright line array of 365nm and 589nm.

[0054] Figure 17 This is a diagram showing the positions of the bright line and the boundary line when there is only one bright line.

[0055] Figure 18 This is a flowchart illustrating the measurement method of stress measuring device 1.

[0056] Figure 19 This is a diagram illustrating the function blocks of the calculation unit 70 of the stress measuring device 1.

[0057] Figure 20 These are photographs of the bright line columns obtained in Examples 1 and 2.

[0058] Figure 21 These are photographs of the bright line columns obtained in Examples 3 and 6.

[0059] Figure 22 This is a diagram illustrating the stress measuring device according to the second embodiment.

[0060] Figure 23 This is a diagram illustrating the light source of the stress measuring device according to the second embodiment.

[0061] Figure 24This is a diagram illustrating the configuration of the optical system of the stress measuring device according to the second embodiment.

[0062] Figure 25 This is a diagram illustrating the stress measuring device according to the third embodiment.

[0063] Figure 26 This is a diagram illustrating a split-type polarizing filter 111.

[0064] Figure 27 This is a diagram illustrating a segmented bandpass filter 112.

[0065] Label Explanation

[0066] 1, 2, 3 Stress measuring device

[0067] 10A, 10B, 10C light sources

[0068] 15 Light guiding components

[0069] 20 Light supply components

[0070] 30 Light-removed components

[0071] 40 Light conversion components

[0072] 50 Polarizing light components

[0073] 60 camera elements

[0074] 70 Computational Unit

[0075] 71 Position Measurement Unit

[0076] 72 Bright line column coincident units

[0077] 73 Calculation of Refractive Index Distribution Unit

[0078] 74 Stress Distribution Calculation Element

[0079] 101A and 101B LED chips

[0080] 103 substrate

[0081] 104 Condensing Lens

[0082] 105 and 112 bandpass filters

[0083] 111 Polarizing filter

[0084] 111a Horizontal Polarizing Plate

[0085] 111b Vertical polarizing plate

[0086] Areas 112a, 112b, 112c, and 112d

[0087] 200 tempered glass

[0088] 210 surface Detailed Implementation

[0089] Hereinafter, with reference to the accompanying drawings, the method of carrying out the invention will be described. In the drawings, the same reference numerals are used to denote the same constituent parts, and sometimes repeated descriptions are omitted.

[0090] <First Implementation Method>

[0091] Figure 1 This is a diagram illustrating the stress measuring device of the first embodiment. Figure 1 As shown, the stress measuring device 1 includes light sources 10A and 10B, a light guiding component 15, a light supply component 20, a light extraction component 30, a light conversion component 40, a polarizing light component 50, an imaging element 60, and a computing unit 70.

[0092] 200 is the tempered glass that is the object being measured. The tempered glass 200 is, for example, glass that has been strengthened by chemical strengthening, air-cooling strengthening, etc., and has a surface layer on the surface 210 side, which has a compressive stress layer and a refractive index distribution.

[0093] Light sources 10A and 10B are light sources capable of emitting light of multiple different wavelengths. Specifically, light sources 10A and 10B are light sources with different wavelengths, and are arranged such that light from either light source 10A or 10B is incident as light ray L onto the surface layer of the tempered glass 200 via the light guiding member 15 and the light supply member 20. Due to the use of interference, the wavelengths of light sources 10A and 10B are preferably single wavelengths that simply display brightness and darkness.

[0094] As the light guiding member 15, a semi-reflective mirror or a dichroic mirror can be used. When a dichroic mirror is used as the light guiding member 15, the transmission efficiency or reflection efficiency can be improved.

[0095] Light sources 10A and 10B are controlled electrically so that only one of them is lit. Alternatively, a mechanical shutter or similar device can be used to allow only light from either light source 10A or 10B to pass through. Other methods, such as mechanically moving the positions of light sources 10A and 10B, can be used as long as the light from light sources 10A and 10B can be switched along the same optical axis to illuminate the light supply member 20.

[0096] The wavelength of one of the light sources 10A and 10B is preferably 1.5 to 2.5 times the wavelength of the other. The reason for setting the wavelength of one of the light sources 10A and 10B to 1.5 to 2.5 times the wavelength of the other is that, as will be explained later, when a bright line array of one wavelength is embedded in a bright line array of the other wavelength, in bright lines of modes with low density and low order, for example, when a bright line of mode 1 with a long wavelength is embedded in a bright line array with a short wavelength, it is possible to obtain a high-precision refractive index distribution or stress distribution located near the middle of mode 1 and mode 2 in the bright line array.

[0097] As light source 10A, a Na lamp, which can easily produce light of a single wavelength, can be used, in this case having a wavelength of 589 nm. In this case, the wavelength of light source 10B is preferably, for example, 400 nm or less. For example, as light source 10B, a mercury lamp with a wavelength shorter than that of a Na lamp can be used. In this case, the wavelength is, for example, the mercury I line, i.e., 365 nm. However, since mercury lamps have a large number of bright lines, it is preferable to use a bandpass filter that allows only the 365 nm line to pass through.

[0098] Alternatively, LEDs (Light Emitting Diodes) can be used as light sources 10A and 10B. In recent years, LEDs of various wavelengths have been developed; however, the spectral width of LEDs, measured at half-amplitude, is greater than 10 nm, exhibiting poor single-wavelength characteristics, and the wavelength varies with temperature. Therefore, it is preferable to use bandpass filters with a narrower spectral width than LEDs.

[0099] With light sources 10A and 10B configured such that the LED passes through a bandpass filter, although Na lamps and mercury lamps do not possess single-wavelength capability, they are preferred because they can use any wavelength from the ultraviolet to the infrared domain. It should be noted that the wavelengths of light sources 10A and 10B do not affect the basic principle of the stress measuring device 1; therefore, light sources other than those illustrated above can also be used. That is, the wavelengths of light sources 10A and 10B are not limited to 589 nm and 365 nm, respectively.

[0100] The light supply member 20 and the light extraction member 30 are mounted in optical contact with the surface 210 of the tempered glass 200, which is the object being measured. The light supply member 20 is equipped with the function of directing light from the light sources 10A and 10B into the surface layer of the tempered glass 200, which has a compressive stress layer. The light extraction member 30 is equipped with the function of directing light propagating within the surface layer of the tempered glass 200 out of the tempered glass 200.

[0101] As the light supply component 20 and the light extraction component 30, prisms made of optical glass can be used, for example. In this case, in order for light to be optically incident and emitted through these prisms on the surface 210 of the tempered glass 200, the refractive index of these prisms needs to be greater than the refractive index of the tempered glass 200.

[0102] Furthermore, the exit angle when light exits from the tempered glass 200 towards the light extraction member 30 is approximately equal to the critical angle generated by the difference in refractive index between the tempered glass 200 and the prism. In order to enable light to be efficiently incident and emitted into the tempered glass 200, the critical angle needs to be 60±15°, more preferably 60±5°. Moreover, it is desirable to select an angle in the tilted surfaces of each prism such that the incident light and the emitted light pass through approximately perpendicularly.

[0103] For example, when the wavelength of the light source 10A is 589nm, the tilt angle of the prism is 60°, and the refractive index of the tempered glass 200 is 1.51, the refractive index of the prism can be set to 1.74.

[0104] Furthermore, the refractive index ratio between the two wavelengths of the prism serving as the light extraction component 30 is preferably the same as the refractive index ratio between the two wavelengths of the tempered glass 200. That is, when the wavelength of the light source 10A is 589 nm and the wavelength of the light source 10B is 365 nm, the refractive index ratio of the prism at 589 nm and 365 nm is preferably the same as the refractive index ratio of the tempered glass 200. This is because, when using the light source 10A and when using the light source 10B, the position of the boundary line described later can be made to be approximately the same.

[0105] As the light supply component 20 and the light extraction component 30, other components with the same function can be used instead of a prism. Furthermore, the light supply component 20 and the light extraction component 30 can be integrated into a single structure. Moreover, to ensure stable optical contact, a liquid (which can be gel-like) with a refractive index between the light supply component 20 and the light extraction component 30 and the tempered glass 200 can be filled.

[0106] An imaging element 60 is arranged in the direction of light emitted from the light extraction member 30, and a light conversion member 40 and a polarizing light member 50 are inserted between the light extraction member 30 and the imaging element 60.

[0107] The light conversion member 40 has the function of converting two light components, which vibrate parallel and perpendicular to the boundary surface between the tempered glass 200 and the light extraction member 30, contained in the light emitted through the light extraction member 30, into two bright line trains, two bright lines, and / or two boundary lines generated at a critical angle by the refractive index difference between the tempered glass 200 and the light supply member 20. For example, a convex lens can be used as the light conversion member 40, but other members with the same function can also be used.

[0108] Furthermore, when using a convex lens as the light conversion component 40, it is preferable to use a combined lens (achromatic lens) with the same focal length at the respective wavelengths of the light sources 10A and 10B.

[0109] Focal lengths are typically used in the range of 100mm to 300mm. Focal length relates to the width of the bright line array that the imaging element 60 can capture at one time. When the focal length is small, although a wide bright line array can be captured at once, it is difficult to capture fine bright line arrays in detail. Conversely, when the focal length is large, this range is the optimal value required for measuring typical tempered glass.

[0110] Figure 2 This is a diagram showing the effect when an achromatic lens is used. Figure 2 (a) is a photograph of the bright line array when the lens position is moved at 365nm with the focus optimally aligned at 589nm using a lens with chromatic aberration. Figure 2 (b) is the image at a wavelength of 365 nm when the focal length is optimally aligned at 589 nm using a combined lens (achromatic lens) with the same focal length at both wavelengths.

[0111] exist Figure 2 In (a), in the image of a bright line array at a focal length of 4% and a focal length of 365nm, the focus is misaligned, making it difficult to determine the accurate position of the bright line. In contrast, in Figure 2 In (b), by using a combination lens (achromatic lens), the focal length difference becomes 0.25%, and the focal points coincide at any wavelength of 589 nm and 365 nm, enabling accurate determination of the bright line position. Thus, the focal length difference between the two wavelengths is preferably as small as ±3%, 2%, 1%, or 0.5%.

[0112] return Figure 1As explained, the polarizing light component 50 is a light separation unit capable of selectively transmitting one of two light components that vibrate parallel to and perpendicular to the boundary surface between the tempering glass 200 and the light extraction component 30. For example, a polarizing plate configured in a rotatable state can be used as the polarizing light component 50, but other components with the same function can also be used. Here, the light component vibrating parallel to the boundary surface between the tempering glass 200 and the light extraction component 30 is S-polarized light, and the light component vibrating perpendicularly is P-polarized light.

[0113] It should be noted that the boundary surface between the tempered glass 200 and the light extraction member 30 is perpendicular to the exit surface of the light emitted from the light extraction member 30 out of the tempered glass 200. Therefore, the light component that vibrates perpendicularly to the exit surface of the light emitted from the light extraction member 30 out of the tempered glass 200 can be referred to as S-polarized light, and the light component that vibrates parallel to it can be referred to as P-polarized light.

[0114] The imaging element 60 is capable of capturing two bright line arrays, two bright lines, and / or two boundary lines generated by light converted by the light conversion member 40. It should be noted that, while maintaining the relative positional relationship between the tempered glass 200, the light extraction member 30, the light conversion member 40, and the imaging element 60, the imaging element 60 can simultaneously or separately capture two bright line arrays, two bright lines, and / or two boundary lines generated by light of multiple different wavelengths.

[0115] The imaging element 60 converts light emitted from the light extraction member 30 and received by the light conversion member 40 and the polarizing member 50 into electrical signals. More specifically, the imaging element 60, for example, converts the received light into electrical signals and can output the brightness value of each of the multiple pixels constituting the image as image data to the processing unit 70. As the imaging element 60, for example, a CCD (Charge Coupled Device) or CMOS (Complementary Metal-Oxide Semiconductor) device can be used, but other devices with the same function can also be used.

[0116] The arithmetic unit 70 has the function of acquiring image data from the imaging element 60 and performing image processing and numerical calculations. The arithmetic unit 70 may also be configured to have other functions (e.g., the function of controlling the amount of light from the light source and the exposure time). The arithmetic unit 70 may be configured to include, for example, a CPU (Central Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory), main memory, etc.

[0117] In this case, the various functions of the arithmetic unit 70 can be implemented by reading programs recorded in ROM or the like into main memory and executing them by the CPU. The CPU of the arithmetic unit 70 can read or store data from RAM as needed. However, some or all of the arithmetic unit 70 can be implemented solely in hardware. Moreover, the arithmetic unit 70 can be physically composed of multiple devices, etc. For example, a personal computer can be used as the arithmetic unit 70.

[0118] In the stress measuring device 1, light L from light source 10A or light source 10B is incident on the surface layer of the tempered glass 200 through light supply member 20 and propagates within the surface layer. Furthermore, as the light L propagates within the surface layer, a pattern is generated through the optical waveguide effect, and it advances along several predetermined paths and is extracted outside the tempered glass 200 by light extraction member 30.

[0119] Furthermore, the light conversion member 40 and the polarization member 50 image bright lines of P-polarized light and S-polarized light for each mode onto the imaging element 60. Image data of the number of P-polarized light and S-polarized light bright lines generated on the imaging element 60 is sent to the calculation unit 70. In the calculation unit 70, the positions of the P-polarized light and S-polarized light bright lines on the imaging element 60 are calculated based on the image data sent from the imaging element 60.

[0120] Furthermore, by switching between two wavelength light sources 10A and 10B, the positions of the bright lines of P-polarized and S-polarized light on the imaging element 60 at each wavelength are calculated based on the image data at each wavelength. Moreover, the relative positional relationships between the strengthening glass 200, the light extraction member 30, the light conversion member 40, and the imaging element 60 are maintained between the images under the two wavelength light sources 10A and 10B and their respective P-polarized and S-polarized light.

[0121] With this structure, in the stress measuring device 1, based on the positions of the bright lines of the P-polarized and S-polarized light of the light sources 10A and 10B, respectively, the refractive index distributions of the P-polarized and S-polarized light in the depth direction from the surface of the tempered glass 200 can be calculated. Furthermore, based on the difference between the calculated refractive index distributions of the P-polarized and S-polarized light and the photoelastic constant of the tempered glass 200, the stress distribution in the depth direction from the surface of the tempered glass 200 can be calculated.

[0122] The calculations, such as those based on the position of bright lines, refractive index distribution, and stress distribution in the image data, can be performed by first recording image data at two wavelengths, and then conducting subsequent calculations based on the recorded image data at the two wavelengths.

[0123] The following describes in more detail the determination of the refractive index distribution and the stress distribution in the stress measuring device 1.

[0124] (Pattern and highlight line)

[0125] Reference Figure 3 and Figure 4 This describes the trajectory and pattern of light rays when they are incident on the surface layer of the tempered glass 200.

[0126] exist Figure 3 In the middle, the tempered glass 200 has a refractive index distribution along the depth direction starting from the surface 210. Figure 3 In the diagram, when the depth from the surface 210 is defined as x, and the refractive index distribution along the depth direction is defined as n(x), the refractive index distribution along the depth direction n(x) is, for example... Figure 4 As shown in the curve. That is, in the tempered glass 200, the refractive index of the surface 210 is high due to chemical strengthening, etc., and decreases as the depth increases. At the depth where the compressive stress layer ends (the deepest part of the compressive stress layer), the refractive index becomes the same as that of the original glass, and in the part deeper than the depth where the compressive stress layer ends, it becomes constant (the refractive index of the original glass).

[0127] Thus, in the surface layer of the tempered glass 200, the refractive index decreases as it moves inward. Therefore, in Figure 3 In the middle, the light ray L incident at a shallow angle relative to surface 210 (in Figure 3 In this example, the light ray incident via the light supply member 20 (which has a refractive index greater than that of the tempered glass 200) gradually approaches parallel to the surface 210, and at the deepest point xt, it reverses from the depth direction toward the surface 210. Furthermore, the light ray after the ray ray trajectory is reversed faces the surface 210 in a shape similar to the shape of the light ray trajectory from the point of incident to the point of reversal, and at least a portion of it is reflected at the surface 210, re-entering the interior of the tempered glass 200.

[0128] The light rays that re-enter the interior of the reinforced glass 200 follow a trajectory of the same shape as those so far, reverse at depth xt, and return to the surface 210. This process is repeated, with the light rays traveling back and forth between the surface 210 and the deepest point xt. Furthermore, the light travels from the surface 210 within a limited space of width xt, thus the light can only propagate as a discrete pattern with finite values.

[0129] That is, light rays with multiple determined paths can propagate on the surface layer of the reinforced glass 200. This phenomenon is called the optical waveguide effect, which is also the principle of light propagation within an optical fiber. The mode of light propagating on surface 210 through the optical waveguide effect and the trajectory of that mode are determined by the refractive index distribution along the depth direction from surface 210.

[0130] Figure 5 This is a diagram illustrating the ray trajectories of each of the multiple modes when they exist. Figure 5 The example shows three modes: Mode 1, Mode 2, and Mode 3, but higher-order modes are also possible. Mode 1, with the lowest order, has the shallowest angle (smallest exit cofactor) when the ray trajectory reflects off surface 210. Furthermore, the deepest point of the ray trajectory differs for each mode; the deepest point xt1 in Mode 1 is the shallowest. As the order of the mode increases, the angle between the ray trajectory and surface 210 when reflecting off surface 210 increases (the exit cofactor increases). Moreover, the deepest point xt2 in Mode 2 is deeper than the deepest point xt1 in Mode 1, and the deepest point xt3 in Mode 3 is deeper than the deepest point xt2 in Mode 2.

[0131] Here, the angle of incidence of a ray relative to a defined surface is the angle between the incident ray and the normal to the defined surface. Conversely, the complementary angle of incidence of a ray relative to a defined surface is the angle between the incident ray and the defined surface. That is, if the angle of incidence of a ray relative to a defined surface is θ, then the complementary angle of incidence of a ray relative to a defined surface is π / 2 - θ. Furthermore, the relationship between the angle of exit and the complementary angle of exit of a ray relative to a defined surface is similar.

[0132] It should be noted that, in Figure 5 The incident light is represented by a single ray, but the incident light has a certain range. Light within this range also has the same complementary angle as the light emitted from surface 210 in the same mode. Furthermore, light generated outside the mode cancels each other out, so no light other than the light corresponding to each mode will be emitted from surface 210.

[0133] In addition, Figure 1 In this structure, the light supply component 20, the light extraction component 30, and the tempered glass 200 have the same shape along the depth direction. Therefore, the light focused by the light conversion component 40 is imaged on the imaging element 60, which serves as the focal plane of the light conversion component 40, and the light corresponding to its mode becomes a bright line along the depth direction.

[0134] Furthermore, the exit angle differs for each mode, therefore, as Figure 6 As shown, the bright lines are arranged sequentially for each pattern, forming a bright line column. It should be noted that bright line columns are usually the same as plain line columns, but in... Figure 1 When the light supply member 20 and the light extraction member 30 are connected as one unit, the direct light from the light source acts as a reference light relative to the emitted light, and sometimes forms a column of dark lines. However, whether it is a column of bright lines or a column of dark lines, the positions of each line are exactly the same.

[0135] Thus, bright lines appear as either bright or dark lines when the mode is valid. Even when the interference color of the bright lines changes depending on the brightness of the reference light, it has no effect on the calculation of the refractive index distribution and stress distribution in this embodiment. Therefore, in this application, both bright and dark lines are represented as bright lines for the sake of simplicity.

[0136] However, the exit cofactor of light propagating within the surface layer, when refracted and exiting beyond the tempered glass 200, is equal to the critical refracted light angle when a medium with a refractive index equal to the effective refractive index nn of the tempered glass 200 at the deepest point of the ray's trajectory within the surface layer comes into contact with the light extraction member 30. The deepest point in each mode can also be interpreted as the point where the light in that mode undergoes total internal reflection.

[0137] Here, when the focal length f of the light conversion component 40, the refractive index np of the light extraction component 30, and the refractive index ng of the tempered glass 200 are set, the relationship between the difference Δn of the effective refractive index nn between a certain mode and the distance ΔS between bright lines is given by the following Equation 1 (Mathematical Equation 1) and Equation 2 (Mathematical Equation 2).

[0138]

Mathematical Formula 1

[0139] Δn=k1·ΔS…(1)

[0140]

Mathematical Formula 2

[0141]

[0142] Therefore, if the position of the effective refractive index at a certain point on the imaging element 60 is known, the effective refractive index of each mode corresponding to the observed bright line can be calculated based on the position of the bright line, that is, the refractive index at the deepest point of the light trajectory within the surface layer of the tempered glass 200.

[0143] (The location of the bright line on the camera element)

[0144] The position of the bright line on the imaging element 60 is determined by the refractive index of the prism, the focal length of the lens, and the effective refractive index of the bright line. Figure 7 This is a diagram illustrating an example of the trajectory of light L from a light source between the tempered glass and the prism. Figure 7 In the above, if the effective refractive index of a certain bright line is set to nr, and the angle of the tilted surface of the prism is set to α, and the angle between the line connecting the center of the imaging element 60 and the point where the light is emitted in the tempered glass 200 (optical axis) and the perpendicular line to the surface of the prism is β, then the following Equation 3 (Mathematical Equation 3) holds true.

[0145]

Mathematical Expression 3

[0146]

[0147] As mentioned earlier, α is typically approximately 60°. That is, if the direction of the optical axis connecting the imaging element and the lens is set at this angle, the effective refractive index nn of the bright line located at the center of the imaging element becomes nr. Moreover, the effective refractive index nn of the bright line offset from the center of the imaging element can be calculated using Equations 1 and 2 based on Δn (=nn-nr) by calculating the difference ΔS between nr and its imaging position.

[0148] (Positions of bright lines at different wavelengths)

[0149] In this embodiment, two different wavelengths are used, but the position of the bright line on the imaging element differs at each wavelength. The position of the bright line at a given wavelength is determined by factors such as the refractive index of the tempered glass, the rate of change of refractive index based on the ion concentration of the tempered glass, the difference in optical path difference caused by the different wavelengths, the difference in photoelastic constants, and the refractive index of the prism. Since these values ​​differ at different wavelengths, even if light from the light source is incident at the same angle, the light trajectories and optical path differences are different, thus the conditions for the mode to hold are different, and the position of the bright line is different.

[0150] Figure 8 It is an example of a bright line array with two wavelengths (1). Figure 8 The upper side shows an example when the light source wavelength is 589nm. Figure 8 The lower side shows an example when the light source wavelength is 365nm, which is P-polarized light. Figure 8 The dashed lines SF1 and SF2 at their respective left ends represent the hypothetical pattern 0 of the surface, which is the position pushed outward from the surface compared to patterns 1 and 2. Figure 8 The dashed lines BP1 and BP2 at their respective right ends represent the boundary locations where brightness changes abruptly. These boundary lines are formed at a critical angle due to the difference in refractive index between the strengthened glass 200 and the light supply component 20. Furthermore, the effective refractive index at the location corresponding to this boundary line is equivalent to the refractive index of the deeper portion of the strengthened glass that has not been reached by the strengthening process. This refractive index is equal to the refractive index of the glass before strengthening, i.e., ng. It should be noted that when Li-containing AlSi-based glasses are chemically strengthened using NaNO3 and KNO3, ng is equal to the glass refractive index ng' at the diffusion depth of K. ng' can be determined through further experiments.

[0151] On the other hand, when considering the case where the boundary line with an effective refractive index of ng in light source 10A is located within the imaging range of the imaging element, Equation 2 is determined by the ratio of np to ng. Furthermore, Equation 3 also aims to select an angle where the incident and outgoing light passes approximately perpendicularly through the tilted surface of the aforementioned prism. Under such conditions, the value of β in Equation 3 is also controlled by the ratio of np to nr, i.e., the ratio of np to ng. Therefore, when switching from light source 10A to light source 10B and changing the wavelength of the light source, according to Equation 3, if the refractive index ratio between the two wavelengths of the prism is the same as the refractive index ratio between the two wavelengths of the tempered glass, then the position of the boundary line is also approximately the same when using the wavelength of light source 10B.

[0152] However, as mentioned earlier, the refractive index of the prism needs to be greater than that of the tempered glass, and selecting a glass with the exact same refractive index ratio as the tempered glass for the prism is industrially difficult. When the refractive index ratios between two wavelengths differ, such as... Figure 8 As shown, the boundary positions of light sources 10A and 10B, represented by dashed lines BP1 and BP2, deviate. If the degree of this deviation is large, they will not enter the same field of view.

[0153] Therefore, while keeping the relative positions of the tempered glass, prism, lens, and imaging element constant, in order to ensure that all bright lines at the wavelengths of the two light sources enter the image of the imaging element 60, the refractive index ratio of the tempered glass and the prism needs to be below a certain value. Let the refractive indices of the tempered glass and the prism at the two wavelengths be nλ1 and nλ2, and let the refractive index ratio between the two wavelengths be v, as shown in Equation 4 (Mathematical Equation 4).

[0154]

Mathematical Expression 4

[0155]

[0156] Furthermore, if the refractive index ratio of the tempered glass and the prism (light extraction component) is set as vg and vp, then Equation 5 (Mathematical Equation 5) is the formula for calculating its tolerance. If the width of the imaging element is set as W and the width of the bright line array is set as S, then the difference between vg and vp, |vp-vg|, preferably satisfies Equation 5.

[0157]

Mathematical Expression 5

[0158]

[0159] The formulas on the left and in the center of Equation 5 are formulas that convert the allowable deviation of the position of the bright line array on the imaging element into the refractive index using Equation 2. Equation 5 only needs to be true if at least one wavelength value is substituted into the central formula and the values ​​of nr, np, and ng recorded on the right, and more preferably it is true for both wavelength values. The right side is an approximation of the change of β when nr / np changes by a small amount according to Equation 3. In the prism, if a glass material that satisfies Equation 5 is selected, the bright line array can be completely captured by the imaging element even at different wavelengths of the light source. The vp of Equation 5 can be calculated based on the Abbe number of the glass material, which is usually disclosed in commercially available optical glass. It should be noted that the width S of the bright line array can be the width from the boundary position to Mode 1.

[0160] Figure 9 This is an example of a bright line array captured by a camera sensor. Figure 9 (a) is an example where equation 5 is not satisfied. Figure 9 (b) is an example that satisfies equation 5. For example... Figure 9 As shown in (a), when Equation 5 is not satisfied, the wavelength of one side (in) Figure 9 (a) Only a portion of the bright line array at 589nm can be captured and cannot be analyzed.

[0161] In such cases, usually as Figure 10 As shown, the position of the imaging element is moved in a manner close to the angle β calculated by Equation 3. For example, from Figure 10 The solid arrows are used to mechanically move the lens and imaging element at an angle that becomes a dashed arrow, thereby enabling the entire bright line column to be captured.

[0162] However, determining the position of bright lines requires an accuracy of less than 1 μm, making it very difficult to move the imaging element with such precision. Therefore, it is preferable to select appropriate imaging element width, lens focal length, prism refractive index, and refractive index ratio to ensure that the entire bright line array enters the image at once. Furthermore, when using two wavelength light sources 10A and 10B and maintaining the relative positions of the tempered glass, prism, lens, and imaging element, a combined lens (achromatic lens) is preferably used to ensure that the focal length is the same for both wavelengths. Regarding the effect of using an achromatic lens, please refer to... Figure 2 That explains it.

[0163] (Methods for converting bright line positions to images of different wavelengths)

[0164] Figure 11 It is an example of a bright line array with two wavelengths (the second one). Figure 11This diagram shows bright line arrays at their respective wavelengths using two light sources 10A and 10B of approximately the same wavelength, while maintaining the relative positions of the tempered glass, the prism (as a light extraction component), the lens (as a light conversion component), and the imaging element. Figure 11 In the light source 10A, the wavelength is 365nm, and in the light source 10B, the wavelength is 589nm.

[0165] according to Figure 11 The bright lines in the 365nm bright line array, with their shorter wavelengths, are more numerous and denser. This is because, as the wavelength shortens, the period of the interference condition also shortens. It should be noted that the meanings of the dashed lines SF1 and SF2, and BP1 and BP2, are different from... Figure 8 The same applies to the case.

[0166] exist Figure 11 In the diagram, the boundary positions shown by the dashed lines BP1 and BP2 are the positions of the critical angles of refractive index determined by the refractive index of the prism and the central portion of the glass that has not been strengthened. However, in the strengthened glass, in the refractive index distribution based on the depth of strengthening, the point where the refractive index of the central portion of the strengthened glass has not been strengthened can be understood as the maximum depth of strengthening.

[0167] At different wavelengths, even for bright lines of the same mode, the effective refractive index and depth of the bright line are different. However, the depth of the surface and the deepest point reached by the reinforcement, i.e. the boundary location, is determined by the reinforcement glass and therefore does not change with wavelength.

[0168] That is, the effective refractive index depth of the hypothetical bright line in mode 0, and its depth from the surface, is 0 μm, but the effective refractive index depth at the surface and from the boundary position are both 365 nm and 589 nm, respectively. Therefore, to replace the position of the 589 nm bright line with that of the 365 nm bright line, the following steps can be taken.

[0169] That is, such as Figure 12 As shown, the bright line positions (dashed line SF1) and boundary bright line positions (dashed line BP1) of mode 0 at 589nm are aligned with the bright line positions (dashed line SF2) and boundary bright line positions (dashed line BP2) of mode 0 at 365nm. The bright line positions of modes other than mode 0 at 589nm coincide with the positions of the bright line columns in the image at 365nm at the same rate. Figure 13 The image shows a bright line column when a bright line at 589nm is embedded in a bright line column at 365nm.

[0170] On the other hand, the conditions for each mode at the two wavelengths, i.e. the formula for the optical path difference of interference, if the optical path difference at 365nm is set to L365 and the number of modes is set to N, and the optical path difference at 589nm is set to L589 and the number of modes is set to N', then according to Equation 8 explained later, they are respectively as in Equation 6 (Mathematical Equation 6).

[0171]

Mathematical Expression 6

[0172] L365=365(N-1 / 2), L589=596(N′-1 / 2)…(6)

[0173] For example, when the light path of the 589nm mode N' is embedded in the 365nm mode that passes through the same light path, if the number of modes under 365nm is expressed as the number of extended modes M after being set to a real number, then according to L365=L589, the number of extended modes M is as shown in Equation 7 (Mathematical Equation 7).

[0174]

Mathematical Expression 7

[0175] M=589 / 365(N′-1 / 2)+1 / 2…(7)

[0176] That is, the bright line of the original 589nm mode 1, if represented by the expanded mode number M, becomes M=1.32 on the 365nm image.

[0177] In that case, Figure 13 The number of expansion modes M of the bright line array becomes 1, 1.32, 2, 2.95, 3... from the left. Table 1 shows the correspondence between the number of modes at 365nm and 589nm and the number of expansion modes M when the bright line array at 589nm coincides with the bright line array at 365nm.

[0178] Table 1

[0179]

[0180] (Calculation of refractive index distribution)

[0181] In this embodiment, the refractive index distribution is calculated using Equation 8 (Mathematical Equation 8). In this embodiment, the refractive index distribution is calculated from bright lines of two wavelengths; however, for ease of explanation, the method for calculating it based on bright lines of a single wavelength will be described here. Equation 8 is a formula derived by the inventors based on technical information described in Non-Patent Document 1, etc. In Non-Patent Document 1, it is assumed that the refractive index distribution changes linearly, and the path of light propagation is approximated as an arc. On the other hand, in this embodiment, the refractive index distribution is set to an arbitrary distribution n(x) in order to obtain the conditions for the validity of a mode under an arbitrary refractive index distribution.

[0182] In Equation 3, θ is the complementary angle of the light ray that travels a small distance dr in a straight line, n0 is the refractive index of the tempered glass surface, Θ is the complementary angle of the light ray incident on the tempered glass, λ is the wavelength of the light ray incident on the tempered glass, and N is the number of modes (e.g., N = 1 if it is mode 1). Furthermore, G1 is the point where the light ray is incident on the tempered glass, F2 is the deepest point of light reversal (xt), and G2 is the point where the light ray reversing at F2 reaches the tempered glass again, which varies for each mode. It should be noted that the first term on the left-hand side pertains to light propagating within the surface layer, and the second term on the left-hand side pertains to light propagating within surface 210.

[0183]

Mathematical Expression 8

[0184]

[0185] Using Equation 8, the rate of change of refractive index of the tempered glass 200 is assumed to be constant between the deepest points of adjacent modes. Starting from the mode with the lowest number of refractive index, the depth of the deepest point of each mode is calculated sequentially, and the overall refractive index distribution can be obtained.

[0186] For example, in Figure 5 In this model, the refractive index, i.e. the effective refractive index, of the surface layer at the deepest depths xt1, xt2, xt3… of each mode is set as n1, n2, n3… Furthermore, the rate of change of refractive index between surface 210-xt1, between xt1-xt2, between xt2-xt3… is set as a straight line, and its rate of change of refractive index is set as α1, α2, α3…

[0187] The ray trajectory in a certain mode n passes through a portion shallower than the deepest point xtn of that mode. Therefore, if the refractive index distribution from the surface to xtn is determined, then its ray trajectory in mode n is uniquely determined. If xt of all modes is known, then the refractive index distribution is uniquely determined. However, according to Equation 8, analytically speaking, it is difficult to directly calculate the refractive index distribution in numerical calculations.

[0188] Therefore, firstly, using Modes 1 and 2, which are the parts closest to surface 210, α1, α2, and xt1, xt2 are determined. In this way, in Mode 3, xt1 and xt2 are known, and the only unknown parameter becomes xt3, thus xt3 can be easily determined. Similarly, if xt4, xt5, ... are determined in the order of Modes 4, 5, ..., then xtn, the deepest point corresponding to all modes, can be determined. Furthermore, the refractive index distribution along the depth direction from surface 210 can be determined.

[0189] Figure 14 This is a diagram illustrating the path of light inside glass. (See reference...) Figure 14This section explains the specific method for calculating the refractive index distribution. First, using ray tracing, the left side of Equation 8 is obtained. Figure 14 In the diagram, the x-direction (longitudinal) is the depth direction of the tempered glass 200, and the y-direction (lateral) is the direction parallel to the surface 210 of the tempered glass 200. Furthermore, the refractive index at depth x is n(x). It should be noted that H is the normal to surface 210.

[0190] Here, the refractive index of the light supply member 20 is set to 1.72, and a ray L incident from the light supply member 20 onto the surface 210 at an incident complementary angle Ψ is considered. Furthermore, the coordinates of the incident point are set as (x0, y0). It should be noted that x0 = 0. At this time, the ray L incident on the interior of the tempered glass 200 is refracted and propagates at an exit complementary angle θ1. At this time, between Ψ and θ1, Snell's law holds.

[0191] Next, inside the tempered glass 200, the trajectory of the light ray L is a curve, but a certain small distance dr is assumed to be a straight line (the distance dr is preferably about 1 / 10 to 1 / 100 of the wavelength). That is, let's assume that the light ray travels in a straight line dr in the direction of the exit complementary angle θ1. At this time, the movement in the x-direction is dx1 = dr·sinθ1, and the movement in the y-direction is dy1 = dr·cosθ1. Moreover, the coordinates of the point of movement are (x1, y1) = (dr·sinθ1, y0 + dr·cosθ1).

[0192] The refractive index of the ray trajectory at the starting point (x0 = 0, y0) is n(0), and the refractive index at the ending point (x1, y1) is n(x1). However, within this ray trajectory, the refractive index is constant at the starting point and changes to n(x1) at the ending point. Therefore, the subsequent ray trajectory follows Snell's law, changing its angle towards the complementary exit angle θ2 and proceeding. The light traveling at the complementary exit angle θ2 travels in a straight line dr, then changes its direction to the complementary exit angle θ3 (not shown) and continues forward. By repeatedly following the ray trajectory, the overall ray trajectory can be determined.

[0193] At this point, for each forward dr, the first term on the left side of Equation 8 is calculated. For example, in the part from coordinate (x0=0, y0) to coordinate (x1, y1), the first term is dr·cosθ1·n(0), which can be easily calculated. Other dr terms can be calculated in the same way. Furthermore, if the first terms obtained for each dr are added together until the ray trajectory returns to surface 210, all the first terms on the left side of Equation 8 are obtained. Moreover, at this point, the distance Σdy that the ray trajectory travels along the y-direction is known. In Equation 8, d... G1G2 =Σdy, Θ=θ1, therefore we can find the second term on the left side of Equation 8, and then find all terms on the left side of Equation 8.

[0194] Next, the method for calculating the refractive index distribution will be explained. First, as shown in Non-Patent Document 1, the refractive index of surface 210 and the deepest point of mode 2 are determined based on the positions of the bright lines in mode 1 and mode 2. Thus, the values ​​of three points—surface 210 (x = 0), the deepest point of mode 1 (xt1), and the deepest point of mode 2 (xt2)—and their refractive indices n0, n1, and n2 can be obtained. However, since the surface is an extrapolation of modes 1 and 2, these three points form a straight line.

[0195] Next, if we assume the deepest point xt3 in mode 3 to be an appropriate value, we can define the refractive index distribution up to xt3. Using the above calculation method, we can calculate the left side of Equation 8 under this distribution. That is, by setting xt3 as the only parameter, we can calculate the left side of Equation 8, and the right side is determined by the degree of the mode, becoming 2.75λ in mode 3.

[0196] Then, using xt3 as a parameter, xt3 can be easily calculated using nonlinear equations such as the bisection method or Newton's method. After calculating xt3, xt4 is calculated based on the position of the bright line in the next mode 4. The same calculation is repeated for all bright lines, thereby calculating the overall refractive index distribution.

[0197] (Calculation of stress distribution)

[0198] Tempered glass has strong in-plane compressive stress, so the refractive index of P-polarized light and the refractive index of S-polarized light deviate from the stress amount due to photoelastic effects. That is, when there is in-plane stress on the surface 210 of tempered glass 200, the refractive index distribution, the way the modes are generated, and the position of the bright lines are different in P-polarized light and S-polarized light.

[0199] Therefore, if the positions of the bright lines in the P-polarized and S-polarized light are known, the refractive index distributions of the P-polarized and S-polarized light can be calculated in reverse. Thus, based on the difference in refractive index distributions between the P-polarized and S-polarized light and the photoelastic constant of the tempered glass 200, the stress distribution σ(x) in the depth direction from the surface 210 of the tempered glass 200 can be calculated.

[0200] Specifically, the stress distribution can be calculated using Equation 9 (Mathematical Equation 9) below. In Equation 9, kc is the photoelastic constant, and Δn... PS (x) represents the difference in refractive index distribution between P-polarized light and S-polarized light. The refractive index distribution of P-polarized light is n. P Refractive index distributions of (x) and S-polarized light n S (x) are obtained discretely, so by approximating the points with straight lines or by calculating an approximate curve using multiple points, the stress distribution can be obtained at any location.

[0201]

Mathematical Expression 9

[0202] σ(x)=Δn PS (x) / kc…(9)

[0203] It should be noted that in the measured stress distribution, the deepest stress layer depth where potassium was replaced is the DOL value. When only potassium exchange was performed, the stress value at the deepest point was the CT value.

[0204] However, the CT and DOL values ​​are calculated based on the small refractive index difference between P-polarized and S-polarized light. Therefore, especially in the region where the refractive index change is small (near the zero cross where the tilt of the refractive index distribution becomes gentle), the refractive index difference between P-polarized and S-polarized light decreases, leading to a larger measurement error. Therefore, the CT value can be calculated using Equation 10 (Mathematical Equation 10) by integrating the calculated stress distribution of the compressive stress layer along the depth direction of the tempered glass 200 with the tensile stress inside the tempered glass 200.

[0205] Here, CS(x) refers to Figure 14 The compressive stress value at position x in the depth direction of the tempered glass 200 is shown. For example, by setting the integration range from the surface 210 of the tempered glass 200 to the center, the CT value can be determined such that the integration result is 0. In this case, the depth of the stress 0 point can be used as the DOL value for calculation.

[0206]

Mathematical Formula 10

[0207]

[0208] Here, the method for calculating the distribution of refractive index and stress along the depth direction based on a bright line column at one wavelength is explained. However, to calculate the refractive index distribution based on bright line columns at two wavelengths, the calculation proceeds in the order of the number of expansion modes when the bright line columns at one wavelength in Table 1 coincide with those at the other wavelength. In this case, the number of expansion modes M is used as the number of modes used in the formula, thereby allowing the calculation of the distribution of refractive index and stress along the depth direction. Furthermore, the total number of bright lines at two wavelengths is significantly increased compared to the number of bright lines at one wavelength, thus obtaining an accurate distribution.

[0209] (Methods for converting bright line positions to images of different wavelengths)

[0210] In the calculation of refractive index distribution and stress distribution, the positions of bright lines and boundary lines are determined. Bright lines can be precisely located because their brightness curves have peaks or troughs. On the other hand, the location of boundary lines is often characterized by a sloping portion of the brightness curve. However, methods for determining boundary line positions based on images typically define the boundary as the location of the sloping portion of the brightness curve. However, due to differences in brightness uniformity between light sources 10A and 10B, the brightness sloping portion of the boundary region differs, making accurate reproduction impossible and hindering the determination of the boundary position.

[0211] In addition, when the rightmost bright line occasionally approaches the boundary, it is difficult to determine the boundary position with particular accuracy. Figure 15 It is a graph showing the image and brightness curves of two types of bright line columns. In Figure 15 In (a), the rightmost bright line (the part indicated by arrow BL1) separates from the boundary position, but in Figure 15 In (b), occasionally the rightmost bright line (the part indicated by arrow BL2) is very close to the boundary position.

[0212] Will Figure 15 When comparing the brightness distribution of the two bright line columns shown, in Figure 15 In (a), the brightness of the boundary changes abruptly, making it easy to determine the boundary location. However, in Figure 15 In (b), the bright line is adjacent to the boundary, so the brightness curve of the bright line overlaps with the brightness curve of the boundary, making it difficult to accurately determine the boundary position.

[0213] In this embodiment, the relative positions of each bright line with respect to the boundary are measured in order to combine bright lines of two wavelengths into a bright line array of any wavelength. However, as mentioned above, if the positions of the bright lines deviate in P-polarized light and S-polarized light, respectively, the positional relationship of the bright lines of the two wavelengths will deviate during the combination, which will become a cause of large errors when calculating the refractive index distribution or stress distribution based on the combined bright line array.

[0214] When calculating the stress distribution of tempered glass from the surface in the depth direction based on the positions of two bright line columns, two bright lines, and / or two boundary lines in light of multiple different wavelengths, data can be referenced from data previously measured using tempered glass of the same composition as the tempered glass being measured.

[0215] For example, using only the boundary position of the inserted side, the bright line position is converted using a standard magnification determined by using tempered glass that has been moderately tempered with the same composition as the tempered glass being measured, and the boundary position difference calculated based on the refractive indices of the tempered glass and the prism at two wavelengths. Furthermore, the boundary position of the bright line column of the converted wavelength is calculated from the boundary position of the bright line column of the inserted wavelength, based on the refractive indices of the prism and the tempered glass at two wavelengths, and this position is used as the boundary position of the converted side for bright line position conversion and insertion.

[0216] The standard glass is preferably strengthened to a certain degree and depth. Furthermore, in the shallow portions produced by modes 1 and 2, unsaturated conditions are preferred in order to make the stress approximately linear.

[0217] (Example of standard magnification and boundary position difference measurement)

[0218] Figure 16 It is a standard reinforced glass bright line array at 365nm and 589nm used to measure the boundary position difference between the magnification and wavelength of a standard.

[0219] Figure 16 The images, starting from the top, are bright line arrays of 365nm P-polarized light, 365nm S-polarized light, 589nm P-polarized light, and 589nm S-polarized light, all maintaining the relative positions of the tempered glass, prism, lens, and imaging element.

[0220] Furthermore, the dashed lines SF (365nm) and SF (589nm) are the positions of the imaginary bright lines of mode 0 on the surface, determined based on the bright lines of mode 1 and mode 2, respectively. These can be determined using a method based on non-patent document 1.

[0221] Next, the distances from mode 0 to the boundary at 365 nm and 589 nm were measured in P-polarized and S-polarized light, respectively, and their ratios were calculated. Figure 16 In the diagram, the distance from the hypothetical mode 0 to the boundary is shown for S-polarized light. d365 and d589 are the distances from the hypothetical mode 0 to the boundary in S-polarized light at various wavelengths. This ratio is then taken as magnification riU and riL. These magnifications riU and riL differ slightly in P-polarized and S-polarized light. This difference is due to the difference in photoelastic effects on the internal stress of the glass generated by strengthening. Regarding the boundary position difference dre, the difference in the position of the boundary line at 365 nm and 589 nm is measured in both P-polarized and S-polarized light, and the average of the results under P-polarized and S-polarized light is used as the boundary position difference.

[0222] Furthermore, the magnification and boundary position difference in the aforementioned standard tempered glass are averaged by measuring multiple standard tempered glasses, enabling the measurement of values ​​with higher precision.

[0223] (A method for calculating other boundary positions from one boundary position)

[0224] In this embodiment, assuming that the relative positions of the prism, tempered glass, lens, and imaging element are constant, the remaining boundary positions are calculated from one of the four boundary positions of the image based on two wavelengths, P-polarized light, and S-polarized light, using the standard magnification and distance difference obtained by the above method.

[0225] Here, using the examples at wavelengths of 365 nm and 589 nm described above, the boundary position of the P-polarized light of the tempered glass being measured is determined. The position deviating from the aforementioned boundary position by the boundary position difference dre calculated above is taken as the boundary position of the P-polarized light at 589 nm.

[0226] Furthermore, the boundary position of S-polarized light is approximately the same as that of P-polarized light, so the boundary position of P-polarized light can be used. Moreover, accuracy can be further improved by correcting the CT value by adjusting the boundary position of S-polarized light. The CS and CT values ​​are pre-measured from the aforementioned standard tempered glass. Based on the ratio of the CS to CT values, the correction amount can be estimated from the distance between the bright line position of mode 1 of S-polarized light and the temporary boundary position. Once the four boundary positions are determined, the refractive index distribution and stress distribution can be calculated using the method described above.

[0227] (Method for measuring stress in a single bright line)

[0228] Figure 17 This is a diagram showing the positions of the bright line and boundary line when there is only one bright line at various wavelengths under different light sources. The bright line is a single line at each wavelength, but it is interpolated into bright line images at different wavelengths using the same method described above. Then, based on the positions of the total two bright lines interpolated into the bright line image at one wavelength, the imaginary bright line position on the surface is calculated.

[0229] When the images of the bright lines at wavelengths of 589nm and 365nm are superimposed, the mode numbers of these two bright lines are 1 and 1.32, respectively. As in the previous method of extrapolating the position of the imaginary mode 0 from modes 1 and 2 at a given wavelength, this time we only need to find the imaginary mode 0 from the bright lines of modes 1 and 1.32.

[0230] If we define the position of the bright line closest to the surface as A, and the position of the second closest bright line as B, then the imaginary bright line position V on the surface can be extrapolated using Equation 11 (Mathematical Equation 11). kw is a constant determined by two wavelengths; in the combination of 365nm and 589nm, kw = 2.56.

[0231]

Mathematical Expression 11

[0232] V=kw×(AB)+A…(11)

[0233] The surface stress is calculated based on the difference between P-polarized and S-polarized light at the position of mode 0 on the extrapolated surface and the photoelastic constant. Furthermore, using the refractive index of the hypothetical mode 0 on the surface and the effective refractive index of the extended mode number 1.32, the depth of mode 1.32 is calculated according to Equation 12 (Mathematical Equation 12). Thus, the dip of the refractive index in the depth direction near the surface can be calculated. The overall refractive index dip is assumed to be a straight line, and the distance to the refractive index at the boundary is calculated, which corresponds to the depth DOL of the potassium-substituted compression layer. It should be noted that Equation 12 calculates the effective refractive index n when the refractive index distribution in the depth direction is a straight line. n Pattern N n The depth d of the deepest point of the bright line n The formula.

[0234]

Mathematical Expression 12

[0235]

[0236] (Measurement procedure)

[0237] Next, refer to Figure 18 and Figure 19 The procedure for measurement is explained. Figure 18 This is a flowchart illustrating the measurement method of stress measuring device 1. Figure 19 This is a diagram illustrating the function blocks of the calculation unit 70 of the stress measuring device 1.

[0238] First, in step S501, light of a first wavelength from the light source 10A is incident on the surface layer of the tempered glass 200 having a compressive stress layer via the light supply member 20 (first light supply step). Next, in step S502, light of the first wavelength generated by the light source 10A that propagates within the surface layer of the tempered glass 200 is emitted out of the tempered glass 200 via the light extraction member 30 (first light extraction step).

[0239] Next, in step S503, the two light components of the first wavelength light emitted from the light extraction member 30 toward the tempered glass 200—one vibrating parallel and the other perpendicular to the boundary surface between the tempered glass 200 and the light extraction member 30—are converted by the light conversion member 40 into two bright line arrays, two bright lines, and / or two boundary lines (first light conversion step). It should be noted that the positions of the boundary lines are different in P-polarized light and S-polarized light, thus resulting in the conversion into two types of boundary lines.

[0240] Next, in step S504, the imaging element 60 captures the two bright line arrays, two bright lines, and / or two boundary lines based on the first wavelength after being converted by the first light conversion process (first imaging process).

[0241] Next, in step S505, the position determination unit 71 of the calculation unit 70 determines the positions of the two bright line columns, the positions of the two bright lines, and / or the positions of the two boundary lines based on the image generated by the light from the light source 10A obtained by the imaging element 60 in the first imaging process (first position determination process).

[0242] Next, in step S506, the light source is switched so that light of the second wavelength from the light source 10B is incident into the surface layer of the tempered glass 200 via the light supply member 20 (second light supply step). Next, in step S507, the light of the second wavelength generated by the light source 10B that propagates within the surface layer of the tempered glass 200 is emitted out of the tempered glass 200 (second light extraction step).

[0243] Next, in step S508, the two light components of the second wavelength light emitted from the light extraction member 30 toward the tempered glass 200—one vibrating parallel and the other perpendicular to the boundary surface between the tempered glass 200 and the light extraction member 30—are converted by the light conversion member 40 into two bright line arrays, two bright lines, and / or two boundary lines (second light conversion process). It should be noted that the positions of the boundary lines are different in P-polarized light and S-polarized light, thus resulting in the conversion into two types of boundary lines.

[0244] Next, in step S509, the imaging element 60 captures the two bright line arrays, two bright lines, and / or two boundary lines based on the second wavelength after being converted by the second light conversion process (second imaging process).

[0245] Next, in step S510, the position determination unit 71 of the calculation unit 70 determines the positions of the two bright line columns, the positions of the two bright lines, and / or the positions of the two boundary lines based on the image generated by the light from the light source 10B obtained by the imaging element 60 in the second imaging process (second position determination process).

[0246] Next, in step S511, the bright line column overlapping unit 72 converts the position of each bright line in the two bright line columns at each wavelength, and inserts it into the bright line column of the other wavelength to make them overlap (bright line column overlapping process).

[0247] Next, in step S512, the refractive index distribution calculation unit 73 calculates the refractive index distribution of the corresponding tempered glass 200 from the surface in the depth direction based on the bright line array of the two overlapping light components (refractive index distribution calculation process).

[0248] Next, in step S513, the stress distribution calculation unit 74 calculates the stress distribution of the reinforced glass 200 from the surface in the depth direction based on the difference in refractive index distribution of the two light components and the photoelastic constant of the glass (stress distribution calculation process).

[0249] It should be noted that, in addition to the arithmetic unit 70 Figure 19 In addition to the structure, it can also have a CT value calculation unit to calculate the CT value and a DOL value calculation unit to calculate the DOL value. In this case, the CT value and DOL value can be calculated based on the stress distribution calculated by the stress distribution calculation unit 74.

[0250] As described above, in the stress measuring apparatus and method of this embodiment, the imaging element 60, while maintaining the relative positional relationships between the tempered glass 200, the light extraction member 30, the light conversion member 40, and the imaging element 60, simultaneously or separately captures two bright line columns, two bright lines, and / or two boundary lines generated by multiple different wavelengths of light. Furthermore, the position measuring unit 71 measures the positions of the two bright line columns, the two bright lines, and / or the two boundary lines based on the images generated by the multiple different wavelengths of light obtained by the imaging element 60. In addition, the stress distribution calculation unit 74 calculates the stress distribution of the tempered glass 200 from the surface in the depth direction based on the positions of the two bright line columns, the two bright lines, and / or the two boundary lines among the multiple different wavelengths of light measured by the position measuring unit 71. Therefore, even for shallow-depth chemically strengthened glass with a very small number of bright lines, where only one bright line is generated depending on the situation, the accuracy of the stress distribution measurement near the surface of the tempered glass can be improved by substantially increasing the number of bright lines.

[0251] Table 2

[0252]

[0253] Table 2 is a table illustrating the appropriate refractive index ratio of the prism in this embodiment, using DT glass (Dragontrail) manufactured by AGC as an example.

[0254] The refractive index of tempered glass (DT glass) is 1.53 at 365 nm and 1.509 at 589 nm, with a refractive index ratio (365 nm / 589 nm) of 1.0139. Furthermore, the maximum strengthening condition for this tempered glass, i.e., the change in refractive index when almost all Na ions in the glass are replaced by K ions, i.e., the refractive index range of the bright lines, is approximately 0.01 for both 365 nm and 589 nm. Therefore, the required refractive index range for imaging (lower limit to upper limit of the bright line range) is 1.53–1.54 at 365 nm and 1.509–1.519 at 589 nm. Moreover, the left side of Equation 5 is 0.0056.

[0255] It should be noted that in the stress measuring device used, the focal length is 166mm, and the width of the imaging part of the imaging element is 3.45μm (1 pixel size) × 1800 pixels = 6.210mm. These are specifications commonly used in conventional stress measuring devices that utilize waveguide light to strengthen glass.

[0256] Example 1 is an example where the refractive index ratio of the tempered glass to the prism does not satisfy Equation 5, making it unsuitable. In Example 1, the prism used is the commonly used Ohara S-LAL10.

[0257] When using the prism of Example 1, the range of refractive index that can be measured, even when it is possible to barely capture a bright line array at 365 nm, is 1.53–1.5484 at 365 nm and 1.4988–1.5169 at 589 nm, according to Equations 1, 2, and 3. The required refractive index range cannot be captured at 589 nm. Moreover, the difference in refractive index ratio is 0.0070, which does not satisfy Equation 5.

[0258] On the other hand, in Example 2, an Ohara S-LAL18 prism was used. In the glass material of the prism in Example 2, the refractive index range for which measurements at 589 nm can be performed is 1.5014 to 1.5194, which is sufficient to capture the desired refractive index range. Furthermore, the difference in refractive index ratios is 0.0052, satisfying Equation 5.

[0259] Figure 20 The photograph shows a bright line array of DT glass that has been strengthened to approximately the maximum extent under the conditions of Examples 1 and 2. Figure 20 (a) is a photograph of Example 1. Figure 20 (b) is a photograph of Example 2.

[0260] like Figure 20 As shown in (b), in Example 2, the entire bright line array at 365nm and 589nm was captured. In contrast, as... Figure 20 As shown in (a), in Example 1, only about half of the 589nm bright line array was captured. It should be noted that the invention is more effective when the number of bright lines is lower; however, for ease of understanding of the deviation in the bright line array, [the following is omitted as it is not directly related to the preceding text]. Figure 20 The image shows a sample with a high number of bright lines.

[0261] As described above, in the stress measuring apparatus and method of this embodiment, while maintaining the relative positional relationships of the tempered glass 200, the light extraction member 30, the light conversion member 40, and the imaging element 60, images based on multiple different wavelengths of light are captured. Furthermore, based on each image generated by the multiple different wavelengths of light, the stress distribution of the tempered glass 200 from its surface in the depth direction is calculated. Therefore, even when the number of bright lines is very small, the accuracy of measuring the stress distribution near the surface of the tempered glass can be improved.

[0262] Furthermore, it is preferable to satisfy Equation 5 as in Example 2, thereby enabling a superior stress measuring device and method. That is, regardless of the strengthening conditions, it is possible to capture all bright line columns at two wavelengths with the optical system fixed, and to perform high-precision stress measurement based on the bright line columns at the two wavelengths.

[0263] According to the stress measurement method described in the first embodiment, for example, stress can be calculated in tempered glass with a CS value of 400 MPa or more and in tempered glass with a DOL value of 3 μm or less when observed by waveguide light.

[0264] Table 3

[0265]

[0266] Table 3 presents the evaluation results for Na-containing AlSi glasses (Examples 3, 4, and 6) and Li-containing AlSi glasses (Examples 5 and 7). Additionally, Figure 21 The photographs are of the bright line columns obtained from Examples 3 and 6. Figure 21 (a) is a photograph of Example 3. Figure 21 (b) is a photograph of Example 6.

[0267] Na-containing AlSi-based glasses were evaluated after being immersed in 100% KNO3 molten salt at 380°C for 15 minutes and then washed, and after being immersed in 100% KNO3 molten salt at 380°C for 3 minutes and then washed. Li-containing AlSi-based glasses were evaluated after being immersed in 100% KNO3 molten salt at 400°C for 60 minutes and then cooled, and after being immersed in 100% KNO3 molten salt at 380°C for 10 minutes and then cooled.

[0268] Regarding the evaluation method, Examples 3-5 were evaluated using the method described in Patent Document 2 (hereinafter referred to as the prior art method), while Examples 6 and 7 were evaluated using the method described in the first embodiment (hereinafter referred to as the present application method). As a result, in Example 3, the prior art method was sufficient for evaluation, but in Examples 4 and 5, the number of bright lines in the P-polarized and S-polarized light was insufficient, making evaluation impossible using the prior art method. On the other hand, in the present application method, evaluation is possible even if the minimum number of bright lines is only one. Therefore, in Examples 6 and 7, the surface compressive stress value (CS value) and the depth (DOL) of the potassium exchange-based compression layer generated by replacing Na with K can be derived. As a result, quality management of glass that cannot be evaluated using the prior art method becomes possible.

[0269] The dashed line BP1 is confirmed in both P-polarized and S-polarized light. If this refractive index difference is set as Δn... PS The stress σ(DOL) is related to the depth DOL of the compressive stress layer that has been ion-exchanged to potassium, and this stress can be calculated using equation (9). However, when the lithium contained in the glass is replaced with sodium, the stress can be calculated as follows: σ(DOL) = f(Δn) PS σ(DOL) can be represented by another function, just like BP2.

[0270] By using the average of the two σ(DOL) values ​​obtained from the dashed lines BP1 and BP2, high-precision σ(DOL) can be obtained.

[0271] Furthermore, when the lithium contained in the glass is replaced with sodium, the stress distribution σ(x) of the sodium ions is related to σ(DOL). Therefore, by using the average or difference of the two σ(DOL), the stress distribution σ(x) of the sodium ions can be predicted with high accuracy.

[0272] <Second Implementation Method>

[0273] In the second embodiment, an example of a stress measuring device with a light source that differs from that in the first embodiment is shown. It should be noted that in the second embodiment, descriptions of components identical to those in the already described embodiments are sometimes omitted.

[0274] Figure 22This is a diagram illustrating the stress measuring device according to the second embodiment. Figure 22 As shown, in the stress measuring device 2, the light source 10C has the function of emitting light of two different wavelengths. The two different wavelengths of light have the function of electrically irradiating simultaneously or separately.

[0275] Figure 23 This diagram illustrates the light source of the stress measuring device according to the second embodiment. The light source 10C includes multiple light-emitting elements arranged adjacent to each other, each emitting light of a different wavelength. Specifically, as light-emitting elements, LED chips 101A and 101B, each capable of emitting light of a different wavelength, are mounted close together on the substrate 103. The shorter the distance between LED chips 101A and 101B, the better, but it is approximately 1 mm depending on the size of the chips.

[0276] like Figure 24 As shown, a condenser lens 104 is configured at the rear end of LED chips 101A and 101B, and a dual-wavelength bandpass filter 105 is configured at the rear end of them.

[0277] Therefore, there are no particular restrictions on the type of light source, as long as it can generate light of different wavelengths, it can be any type.

[0278] <Third Implementation Method>

[0279] In the third embodiment, an example of a stress measuring device with a light source that differs from that in the second embodiment is shown. It should be noted that in the third embodiment, descriptions of components identical to those in the already described embodiments are sometimes omitted.

[0280] Figure 25 This diagram illustrates the stress measuring apparatus according to the third embodiment. In addition to the structure of the second embodiment, the stress measuring apparatus 3 of the third embodiment also includes a segmented polarizing filter 111 and a segmented bandpass filter 112 at the front end of the imaging element 60. Therefore, by taking a single image, bright line images of P-polarized light and S-polarized light of two wavelengths can be obtained simultaneously. It should be noted that, unlike the second embodiment, the bandpass filter may not be present at the rear end of the light source 10C.

[0281] Figure 26 This is a diagram illustrating a split-type polarizing filter 111. Figure 26The polarizing filter 111 shown is a light-separating unit having a region that allows the light component vibrating parallel to the boundary surface to pass through and a region that allows the light component vibrating perpendicular to the boundary surface to pass through, and is disposed between the imaging element 60 and the bandpass filter 112. Specifically, the polarizing filter 111 is divided at its center line into a horizontal polarizing plate 111a with the polarization direction horizontal and a vertical polarizing plate 111b with the polarization direction perpendicular. Figure 26 In the image, the arrow indicates the direction of polarized light.

[0282] Figure 27 This is a diagram illustrating a segmented bandpass filter 112. Figure 27 The bandpass filter 112 shown is a light-splitting unit that allows one or the other of two wavelengths emitted from the light source to pass through and is used to improve monochromaticity. It is divided into four regions 112a to 112d. The bandpass filter 112 has regions 112a and 112c that allow only wavelength λa of the light from the multiple wavelengths of the light source to pass through, and regions 112b and 112d that allow only wavelength λb of the other wavelength to pass through.

[0283] Regions 112a and 112b correspond to the horizontal polarizing plate 111a, and regions 112c and 112d correspond to the vertical polarizing plate 111b. That is, light with wavelength λa passing through one region 112a of the bandpass filter 112 and light with wavelength λb passing through the other region 112b of the bandpass filter 112 are incident on the horizontal polarizing plate 111a. Furthermore, light with wavelength λa passing through one region 112c of the bandpass filter 112 and light with wavelength λb passing through the other region 112d of the bandpass filter 112 are incident on the vertical polarizing plate 111b.

[0284] Thus, the stress measuring device 3 is equipped with a polarizing filter 111 and a bandpass filter 112, thereby enabling the capture of bright line images of two wavelengths of P-polarized light and S-polarized light in a single shot.

[0285] The preferred embodiments have been described in detail above, but are not limited to the embodiments described above. Various modifications and substitutions can be made to the embodiments described above without departing from the scope of the claims.

Claims

1. A stress measuring device for tempered glass, characterized in that, have: A light source, capable of emitting light of multiple different wavelengths; A light supply component that directs light from the light source into the surface layer of the reinforced glass having a compressive stress layer; The light extraction component causes the light propagating within the surface layer to be emitted outside the reinforced glass; The light conversion component converts two light components, which vibrate parallel and perpendicular to the boundary surface between the tempered glass and the light extraction component, contained in the light emitted through the light extraction component, into two bright line columns, two bright lines, and / or two boundary lines generated by the critical angle using the refractive index difference between the tempered glass and the light supply component. The imaging element captures the two types of bright line arrays, the two types of bright lines, and / or the two types of boundary lines; and The position determination unit determines the positions of the two bright line columns, the positions of the two bright lines, and / or the positions of the two boundary lines from the images generated by the plurality of different wavelengths of light obtained through the imaging element. While maintaining the relative positions of the tempered glass, the light extraction component, the light conversion component, and the imaging element, the imaging element simultaneously or separately captures the two types of bright line arrays, the two types of bright lines, and / or the two types of boundary lines generated by the multiple different wavelengths of light. Based on the positions of the two bright line columns, the positions of the two bright lines, and / or the positions of the two boundary lines in multiple different wavelengths of light measured by the position measuring unit, the multiple bright line columns of different wavelengths are synthesized, thereby calculating the stress of the tempered glass in the depth direction from the surface. Synthesizing the multiple bright line arrays of different wavelengths involves representing the pattern of one wavelength as an expanded pattern number after setting the pattern number of the other wavelength to a real number.

2. The stress measuring device for tempered glass according to claim 1, characterized in that, At at least one of the multiple different wavelengths, Equation 5 is satisfied. 【Mathematical Expression 5】 In Equation 5, k1 is a parameter, f is the focal length of the optical conversion element, and n is the focal length of the optical conversion element. p The refractive index of the optically extracted component, n g W: Refractive index of the tempered glass; S: Width of the imaging element; V: Width of the bright line array. p The refractive index ratio of the light extraction component at multiple different wavelengths, v g The refractive index ratio of tempered glass at multiple different wavelengths.

3. A stress measuring device for tempered glass, characterized in that, have: A light source, capable of emitting light of multiple different wavelengths; A light supply component that directs light from the light source into the surface layer of the reinforced glass having a compressive stress layer; The light extraction component causes the light propagating within the surface layer to be emitted outside the reinforced glass; The light conversion component converts two light components, which vibrate parallel and perpendicular to the boundary surface between the tempered glass and the light extraction component, contained in the light emitted through the light extraction component, into two bright line columns, two bright lines, and / or two boundary lines generated by the critical angle using the refractive index difference between the tempered glass and the light supply component. The imaging element captures the two types of bright line arrays, the two types of bright lines, and / or the two types of boundary lines; and The position determination unit determines the positions of the two bright line columns, the positions of the two bright lines, and / or the positions of the two boundary lines from the images generated by the plurality of different wavelengths of light obtained through the imaging element. While maintaining the relative positions of the tempered glass, the light extraction component, the light conversion component, and the imaging element, the imaging element simultaneously or separately captures the two types of bright line arrays, the two types of bright lines, and / or the two types of boundary lines generated by the multiple different wavelengths of light. Based on the positions of the two bright line columns, the positions of the two bright lines, and / or the positions of the two boundary lines in multiple different wavelengths of light measured by the position measuring unit, the stress of the tempered glass in the depth direction from the surface is calculated. At at least one of the multiple different wavelengths, Equation 5 is satisfied. 【Mathematical Expression 5】 In Equation 5, k1 is a parameter, f is the focal length of the optical conversion element, and n is the focal length of the optical conversion element. p The refractive index of the optically extracted component, n g W: Refractive index of the tempered glass; S: Width of the imaging element; V: Width of the bright line array. p The refractive index ratio of the light extraction component at multiple different wavelengths, v g The refractive index ratio of tempered glass at multiple different wavelengths.

4. The stress measuring device for tempered glass according to claim 1 or 3, characterized in that, The light conversion component is a combination lens in which the difference in focal length at multiple wavelengths is less than ±3%.

5. The stress measuring device for tempered glass according to claim 1 or 3, characterized in that, The wavelength of one of the light sources is 1.5 to 2.5 times that of the other.

6. The stress measuring device for tempered glass according to claim 1 or 3, characterized in that, When calculating the stress distribution of the tempered glass from the surface in the depth direction based on the positions of the two bright line columns, the positions of the two bright lines, and / or the positions of the two boundary lines in the plurality of different wavelengths of light, reference is made to data previously measured by tempered glass with the same composition as the tempered glass being measured.

7. The stress measuring device for tempered glass according to claim 1 or 3, characterized in that, The light source comprises multiple light-emitting elements arranged adjacent to each other, emitting light of different wavelengths.

8. The stress measuring device for tempered glass according to claim 1 or 3, characterized in that, The front section of the imaging element has a first light separation unit, which has a region that allows only the wavelength of light from one of the plurality of light sources to pass through and a region that allows only the wavelength of the other light source to pass through.

9. The stress measuring device for tempered glass according to claim 8, characterized in that, A second light separation unit is provided between the imaging element and the first light separation unit. The second light separation unit has a region that allows the light component that vibrates parallel to the boundary surface to pass through and a region that allows the light component that vibrates perpendicular to the boundary surface to pass through.

10. A method for determining the stress of tempered glass, characterized in that, include: In the first light supply process, light of the first wavelength is incident through the light supply component into the surface layer of the reinforced glass with a compressive stress layer. In the first light extraction process, light of the first wavelength propagating within the surface layer is emitted out of the tempered glass via a light extraction member. In the first light conversion process, the two light components contained in the first wavelength light emitted out of the tempered glass, which vibrate parallel and perpendicular to the boundary surface between the tempered glass and the light extraction member, are converted by the light conversion member into two bright line columns, two bright lines, and / or two boundary lines generated by the critical angle using the refractive index difference between the tempered glass and the light supply member. The first imaging process involves capturing images of the two bright line arrays, the two bright lines, and / or the two boundary lines based on the first wavelength using an imaging element. The first position determination step involves determining the positions of the two bright line columns, the positions of the two bright lines, and / or the positions of the two boundary lines based on the image generated by the light of the first wavelength obtained through the first imaging step. The second light supply process involves directing light of a second wavelength into the surface layer via the light supply component. The second light extraction process causes the light of the second wavelength propagating within the surface layer to be emitted out of the tempered glass via the light extraction member; The second light conversion process converts the two light components of the second wavelength light emitted out of the tempered glass, which vibrate parallel and perpendicular to the boundary surface between the tempered glass and the light extraction member, into the two bright line columns, the two bright lines, and / or the two boundary lines. The second imaging process involves capturing images of the two bright line arrays, the two bright lines, and / or the two boundary lines generated by the second wavelength using the imaging element; and The second position determination step involves determining the positions of the two bright line columns, the positions of the two bright lines, and / or the positions of the two boundary lines from the image generated by the light of the second wavelength obtained through the second imaging step. In the first and second imaging processes, while maintaining the relative positional relationships of the tempered glass, the light extraction component, the light conversion component, and the imaging element, the two types of bright line arrays, the two types of bright lines, and / or the two types of boundary lines generated by multiple different wavelengths of light are simultaneously or separately captured. Based on the positions of the two bright line columns, the positions of the two bright lines, and / or the positions of the two boundary lines in multiple different wavelengths of light measured through the first and second position measurement steps, the multiple bright line columns of different wavelengths are synthesized, thereby calculating the stress of the tempered glass in the depth direction from the surface. Synthesizing the multiple bright line arrays of different wavelengths involves representing the pattern of one wavelength as an expanded pattern number after setting the pattern number of the other wavelength to a real number.

11. The method for determining the stress of tempered glass according to claim 10, characterized in that, Regardless of whether the first wavelength or the second wavelength of light is used, the stress in the depth direction from the surface of the tempered glass is calculated as the minimum number of bright lines observed through the two light components being one.

12. The method for determining the stress of tempered glass according to claim 11, characterized in that, One of the first wavelength and the second wavelength is below 400 nm.

Images