Apparatus and method for measuring stress of tempered glass

Abstract

To provide a stress measurement device of reinforced glass capable of improving measurement accuracy for stress distribution near the surface of a reinforced glass.SOLUTION: The stress measurement device of reinforced glass comprises: a light source having a function to emit light of a plurality of different wavelengths; an optical conversion member 40 emitting light propagating through a surface layer of a reinforced glass 200 including a compression stress layer outside the reinforced glass 200, and converting two types of light components oscillating in parallel and perpendicular to the surface of the reinforced glass 200 at a critical angle into two types of boundary lines; and an image pick-up device 60. The image pick-up device 60 executes imaging, in a state where the positional relationship among the reinforced glass 200, a light extraction member 30 and the image pick-up device 60 is maintained, and calculates the stress of the reinforced glass from the surface to depth direction on the basis of a position of two types of bright line rows, a position of the two types of bright lines, and / or a position of the two types of boundary lines in the light of a plurality of different wavelengths measured by position determination means.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a device for measuring stress in tempered glass, a method for measuring stress in tempered glass, and tempered glass. [Background technology]

[0002] Glass is often used in the display and housing of electronic devices such as mobile phones and smartphones. As electronic devices have become thinner and lighter in recent years, thinner glass is also being required. The thinner the glass, the weaker it becomes. Therefore, to increase the strength of glass, so-called chemically strengthened glass is used, which is created by forming a surface layer (ion-exchange layer) on the glass surface through ion exchange, generating compressive stress, and then optical methods are used to measure the surface stress to confirm that the glass has been properly strengthened before it is shipped to the market.

[0003] One example of a technique for measuring the stress in the surface layer of tempered glass is a technique (hereinafter referred to as "nondestructive measurement technique") that uses the optical waveguiding effect and the photoelastic effect to nondestructively measure the compressive stress in the surface layer when the refractive index of the surface layer of tempered glass is higher than the refractive index of the interior of the glass. In this nondestructive measurement technique, monochromatic light is incident on the surface layer of the tempered glass, generating multiple modes through the optical waveguiding effect, and light with a fixed ray trajectory is extracted in each mode and imaged into emission lines corresponding to each mode using a convex lens. Note that there are as many imaged emission lines as there are modes.

[0004] Furthermore, this nondestructive measurement technology is configured so that the light extracted from the surface layer can be observed as bright lines for two types of light components, those whose vibration directions are horizontal and vertical to the exit surface. Utilizing the property that the light of the lowest order, mode 1, passes through the side of the surface layer closest to the surface, the refractive index for each of the two types of light components is calculated from the positions of the bright lines corresponding to mode 1 of the two types of light components, and the stress near the surface of the tempered glass is determined from the difference between the two refractive indices and the photoelastic constant of the glass (see, for example, Patent Document 1).

[0005] On the other hand, based on the principles of the above-mentioned non-destructive measurement technology, a method has been proposed in which the stress at the outermost surface of the glass (hereinafter referred to as the surface stress value) is calculated by extrapolation from the positions of the emission lines corresponding to Mode 1 and Mode 2, and the depth of the compressive stress layer is calculated from the total number of emission lines, assuming that the refractive index distribution of the surface layer changes linearly (see, for example, Patent Document 2 and Non-Patent Document 1).

[0006] Furthermore, a method has been proposed in which the tensile stress CT inside the glass is defined based on the surface stress value measured by the above-mentioned measurement technique using surface guided light and the depth of the compressive stress layer, and the strength of the tempered glass is controlled by the CT value (see, for example, Patent Document 3). In this method, the tensile stress CT is calculated using the formula "CT = (CS × DOL) / (t × 1000 - 2 × DOL)" (Equation 0). Here, CS is the surface stress value (MPa), DOL is the depth (unit: μm) of the compressive stress layer caused by ion-exchanging sodium for potassium, and t is the plate thickness (unit: mm).

[0007] Generally, if no external force is applied, the total stress is 0. Therefore, the value obtained by integrating the stress generated by chemical strengthening in the depth direction generates a substantially uniform tensile stress so that it is balanced in the central part that is not chemically strengthened.

[0008] However, chemically strengthened glass has become more diverse due to improvements in strength and performance, and conventional stress measurement methods are no longer sufficient for evaluation.

[0009] For example, there are tempered glasses in which lithium-containing glass is exchanged with two types of ions, potassium and sodium, to control the stress distribution, and chemically tempered glasses in which transparent crystallized glass is exchanged with ions.

[0010] In chemically strengthened lithium-containing glass, conventional optical stress measurement devices can evaluate the stress layer near the surface where lithium and sodium have been exchanged for potassium, but cannot evaluate the internal stress layer where lithium has been exchanged for sodium. Therefore, the compressive stress does not become zero at the depth DOL of the compressive stress layer where ions have been exchanged for potassium, and the depth DOC (unit: μm) where the compressive stress becomes zero cannot be measured using stress measurement devices that use guided wave light on the surface.

[0011] A method has also been proposed in which the stress distribution on the glass surface side beyond the glass depth (DOL_TP) where the stress distribution is significantly bent due to the influence of these two stress layers, and the stress distribution on the glass deeper side beyond DOL_TP is predicted based on the measurement results (measurement image) of the stress distribution on the glass surface side (see, for example, Patent Document 4). However, this method has the problem of poor measurement reproducibility because the stress distribution on the glass deeper side beyond DOL_TP is not actually measured.

[0012] Since crystallized glass must be transparent, especially for use in displays, the crystallized glass used here is crystallized glass with crystal grains much smaller than the wavelength of visible light, and is transparent in the visible range. Therefore, the surface stress formed during the chemical strengthening process can be measured using a conventional optical stress measurement device.

[0013] Therefore, in order to maintain the quality of the diversified chemically strengthened glass, it is necessary to measure and manage the distribution of stress deep inside and the crystalline state of crystallized glass.

[0014] In recent years, lithium aluminosilicate glasses have been attracting attention as they are easy to ion exchange, can be chemically strengthened in a short time, and can produce high surface stress values ​​and a deep stress layer.

[0015] This glass is then chemically strengthened by immersing it in a high-temperature molten salt mixture of sodium nitrate and potassium nitrate. Because the concentrations of both sodium and potassium ions in the molten salt are high, they exchange with the lithium ions in the glass. However, because sodium ions diffuse more easily into the glass, the lithium ions in the glass are first exchanged with the sodium ions in the molten salt.

[0016] The refractive index of glass is lower when sodium ions are ion-exchanged with lithium ions, and higher when potassium ions are ion-exchanged with either lithium ions or sodium ions. In other words, compared to the non-ion-exchanged portions of the glass, the ion-exchanged regions near the surface of the glass have a higher potassium ion concentration, while the sodium ion concentration increases in deeper ion-exchanged regions. Therefore, the refractive index of ion-exchanged glass decreases with depth near the outermost surface, but increases with depth from a certain depth to the non-ion-exchanged regions.

[0017] Therefore, the stress measurement device using the surface guided light mentioned above can only measure the stress value or stress distribution on the outermost surface, and cannot measure the stress distribution in deeper areas, making it impossible to know the depth of the stress layer, CT value, or overall stress distribution. As a result, it was not possible to develop the appropriate chemical strengthening conditions, and it was also impossible to control the quality of manufacturing.

[0018] Furthermore, when aluminosilicate glass or soda glass is chemically strengthened after air-cooling, the stress distribution or stress value of the chemically strengthened portion can be measured using the aforementioned stress measurement device that utilizes surface guided light. However, the refractive index change in the portion that has only been air-cooled and not chemically strengthened is small, and cannot be measured using the aforementioned stress measurement device that utilizes surface guided light. As a result, it was not possible to determine the depth of the stress layer, the CT value, or the overall stress distribution. As a result, it was not possible to develop a method to find the appropriate chemical strengthening conditions, and it was also not possible to control the quality of the manufacturing process.

[0019] To address these issues, a stress measurement device capable of measuring the stress distribution of tempered glass using scattered light from a laser beam has been proposed (see, for example, Patent Document 5). This device makes it possible to measure the stress distribution of tempered glass from the surface to deep portions, regardless of the refractive index distribution in the depth direction. This stress measurement device includes a polarization phase difference variable member that varies the polarization phase difference of the laser beam by one or more wavelengths relative to the wavelength of the laser beam, and an image sensor that captures multiple images at predetermined time intervals of scattered light emitted when the laser beam with the varied polarization phase difference is incident on the tempered glass, thereby acquiring multiple images. The device then measures the periodic brightness change of the scattered light using the multiple images, calculates the phase change of the brightness change, and calculates the stress distribution in the depth direction from the surface of the tempered glass based on the phase change. [Prior art documents] [Patent documents]

[0020] [Patent Document 1] Japanese Patent Application Publication No. 53-136886 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-142600 [Patent Document 3] Special Publication No. 2011-530470 [Patent Document 4] US Patent Publication No. 2016 / 0356760 [Patent Document 5] International Publication No. 2018 / 056121 [Non-patent literature]

[0021] [Non-Patent Document 1] Yogyo-Kyokai-Shi (Ceramics Association Journal) 87{3}1979 Summary of the Invention [Problem to be solved by the invention]

[0022] In recent years, cover glass used in foldable smartphones and other devices has a thickness of, for example, 50 μm or less. Tempered glass is often used for such thin glass, but the chemical strengthening depth of tempered glass is, for example, 10 μm or less. In principle, the thinner the glass plate, the deeper the chemical strengthening depth. Furthermore, even in lithium-containing aluminosilicate glass, which is widely used as tempered glass, chemical strengthening by replacing lithium with sodium tends to increase tensile energy due to the deep substitution depth. Therefore, when chemical strengthening with sodium and potassium is performed following or simultaneously with chemical strengthening by replacing lithium with sodium, the chemically strengthened surface layer, with a high potassium ion concentration, tends to be shallower to suppress tensile energy while increasing surface compressive stress. Furthermore, when chemically strengthening crystallized glass, due to the inherent strength of crystallized glass, emphasis is placed on preventing surface scratches, and only the outermost surface is often chemically strengthened to suppress tensile energy. Thus, reducing the substitution depth by chemical strengthening with sodium and potassium tends to suppress tensile energy.

[0023] When measuring the stress distribution of tempered glass with shallow chemical strengthening depths, such as those described above, using a stress measurement device that uses guided light, the number of emission lines generated is very small; in some cases, only one emission line (mode 1, described below) is generated for some tempered glass. Shortening the wavelength of the guided light source is an effective way to increase the number of emission lines, but when the wavelength is shorter than 350 nm, the transmittance of most optical glass and tempered glass decreases, causing the optical system of the measurement device to malfunction or making it impossible to observe the guided light, so there are limitations to how many emission lines can be increased. Therefore, it has been impossible to accurately measure the stress distribution near the surface of tempered glass with extremely shallow chemical strengthening, making quality control impossible, and no such products have been produced.

[0024] The present invention has been made in view of the above points, and has an object 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. [Means for solving the problem]

[0025] The tempered glass stress measuring device includes a light source having a function of emitting light of a plurality of different wavelengths, a light supplying member that causes light from the light source to enter a surface layer of the tempered glass having a compressive stress layer, a light extraction member that causes the light that has propagated through the surface layer to exit the tempered glass, a light converting member that converts two types of light components that are contained in the light that has exited through the light extraction member and vibrate parallel and perpendicular to the boundary surface between the tempered glass and the light extraction member into two types of bright line trains, two types of bright lines, and / or two types of boundary lines that occur at a critical angle due to a refractive index difference between the tempered glass and the light supplying member, an imaging element that images the two types of bright line trains, the two types of bright lines, and / or the two types of boundary lines, and a sensor that senses the intensity of the light from the imaging element. and a position measurement means for measuring the positions of the two types of bright line rows, the positions of the two types of bright lines, and / or the positions of the two types of boundary lines from each image obtained by the element using light of the plurality of different wavelengths, wherein the imaging element simultaneously or separately images the two types of bright line rows, the two types of bright lines, and / or the two types of boundary lines obtained by light of the plurality of different wavelengths while maintaining the relative positions of the strengthened glass, the light extraction member, the light conversion member, and the imaging element, and calculates stress from the surface of the strengthened glass in the depth direction based on the positions of the two types of bright line rows, the positions of the two types of bright lines, and / or the positions of the two types of boundary lines in light of the plurality of different wavelengths measured by the position measurement means. [Effects of the Invention]

[0026] According to the disclosed technique, it is possible to provide a stress measuring device for tempered glass that can improve the measurement accuracy of the stress distribution near the surface of tempered glass. [Brief explanation of the drawings]

[0027] [Figure 1] FIG. 1 is a diagram illustrating a stress measuring device according to a first embodiment. [Figure 2] FIG. 10 is a diagram showing the effect of using an achromatic lens. [Figure 3] FIG. 10 is a diagram illustrating modes. [Figure 4] FIG. 2 is a diagram illustrating a refractive index distribution of a surface layer of tempered glass. [Figure 5] FIG. 10 is a diagram illustrating the ray trajectories of each mode when multiple modes exist. [Figure 6] FIG. 10 is a diagram illustrating an example of an emission line sequence corresponding to a plurality of modes. [Figure 7] FIG. 2 is a diagram showing an example of a trajectory of light from a light source between a tempered glass and a prism. [Figure 8] This is an example (part 1) of a series of emission lines at two wavelengths. [Figure 9] This is an example of an array of bright lines captured by an image sensor. [Figure 10] FIG. 10 is a diagram illustrating the movement of an imaging element. [Figure 11] This is an example (part 2) of a two-wavelength emission line array. [Figure 12] This is a diagram (part 1) explaining the superposition of emission line rows. [Figure 13] FIG. 2 is a diagram (part 2) explaining the superposition of emission line rows. [Figure 14] FIG. 1 is a diagram illustrating ray trajectories inside glass. [Figure 15] FIG. 1 shows images of two types of bright line trains and their brightness curves. [Figure 16] Standard tempered glass has emission lines of 365nm and 589nm. [Figure 17] FIG. 10 is a diagram showing the positions of the bright line and the boundary line when there is one bright line. [Figure 18] 1 is a flowchart illustrating a measurement method of the stress measurement apparatus 1. [Figure 19] FIG. 2 is a diagram illustrating an example of functional blocks of a calculation unit 70 of the stress measurement device 1. [Figure 20] These are photographs of the bright line sequences obtained in Examples 1 and 2. [Figure 21] These are photographs of the bright line sequences obtained in Examples 3 and 6. [Figure 22] FIG. 10 is a diagram illustrating a stress measuring device according to a second embodiment. [Figure 23]FIG. 10 is a diagram illustrating a light source of the stress measuring apparatus according to the second embodiment. [Figure 24] FIG. 10 is a diagram illustrating the arrangement of an optical system of a stress measurement apparatus according to a second embodiment. [Figure 25] FIG. 10 is a diagram illustrating a stress measuring device according to a third embodiment. [Figure 26] FIG. 10 is a diagram illustrating a split polarizing filter 111. [Figure 27] FIG. 10 is a diagram illustrating a split-type bandpass filter 112. DETAILED DESCRIPTION OF THE INVENTION

[0028] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following describes the preferred embodiments of the present invention with reference to the accompanying drawings. In the drawings, the same components are designated by the same reference numerals, and redundant explanations may be omitted.

[0029] First Embodiment Fig. 1 is a diagram illustrating a stress measuring device according to the first embodiment. As shown in Fig. 1, the stress measuring device 1 includes light sources 10A and 10B, a light introducing member 15, a light supplying member 20, a light extracting member 30, a light converting member 40, a polarizing member 50, an imaging element 60, and a computing unit 70.

[0030] Reference numeral 200 denotes a tempered glass to be measured. The tempered glass 200 is glass that has been subjected to a tempering process, for example, by a chemical tempering method or an air-cooling tempering method, and is provided with a surface layer on the surface 210 side, which has a compressive stress layer with a refractive index distribution.

[0031] The light sources 10A and 10B are light sources capable of emitting light of multiple different wavelengths. Specifically, the light sources 10A and 10B have different wavelengths, and are arranged such that light from either the light source 10A or the light source 10B is incident as light ray L on the surface layer of the tempered glass 200 via the light supply member 20 through the light introducing member 15. To utilize interference, it is preferable that the wavelengths of the light sources 10A and 10B are each a single wavelength that results in a simple bright / dark display.

[0032] For example, a half mirror or a dichroic mirror can be used as the light introducing member 15. When a dichroic mirror is used as the light introducing member 15, the transmission efficiency or reflection efficiency can be increased.

[0033] The light sources 10A and 10B are electrically controlled so that only one of them is turned on. Alternatively, a mechanical shutter or the like may be used to transmit only one of the light sources 10A and 10B. As long as the light from the light sources 10A and 10B can be irradiated onto the light supply member 20 along the same optical axis and can be switched, other methods may be used, such as mechanically moving the positions of the light sources 10A and 10B.

[0034] 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 described later, when fitting one of the emission line trains of two wavelengths to the other emission line train, the emission line of a low-order mode with a low density of the emission line train, for example, when fitting the emission line of mode 1 of a long wavelength to the emission line train of a short wavelength, can be positioned near the middle between mode 1 and mode 2 of the emission line train of the short wavelength, thereby obtaining a highly accurate refractive index distribution or stress distribution.

[0035] As light source 10A, for example, a Na lamp, which can easily produce light of a single wavelength, can be used, and in this case the wavelength is 589 nm. In this case, the wavelength of light source 10B is preferably, for example, 400 nm or less. For example, a mercury lamp, which has a shorter wavelength than a Na lamp, can be used as light source 10B. In this case, the wavelength is, for example, 365 nm, which is the mercury I line. However, since mercury lamps have many emission lines, it is preferable to use them through a bandpass filter that transmits only the 365 nm line.

[0036] Alternatively, light sources 10A and 10B may be LEDs (Light Emitting Diodes). In recent years, LEDs with many wavelengths have been developed, but the spectral width of an LED is 10 nm or more at half maximum, which makes them poorly single-wavelength, and the wavelength changes with temperature. For this reason, it is preferable to use an LED through a bandpass filter with a narrower spectral width than the LED.

[0037] When the light sources 10A and 10B are configured as LEDs passed through bandpass filters, they do not have the same single wavelength characteristics as sodium lamps or mercury lamps, but are preferable in that any wavelength from the ultraviolet region to the infrared region can be used. Note that the wavelengths of the light sources 10A and 10B do not affect the basic principle of measurement of the stress measurement apparatus 1, so light sources with wavelengths other than those exemplified above may also be used. In other words, the wavelengths of the light sources 10A and 10B are not limited to 589 nm and 365 nm.

[0038] The light supplying member 20 and the light extracting member 30 are placed in optical contact with the surface 210 of the tempered glass 200, which is the object to be measured. The light supplying member 20 has a function of making light from the light sources 10A and 10B incident on the surface layer, which has a compressive stress layer, of the tempered glass 200. The light extracting member 30 has a function of making light that has propagated through the surface layer of the tempered glass 200 exit the tempered glass 200.

[0039] For example, prisms made of optical glass can be used as the light supply member 20 and the light extraction member 30. In this case, the refractive index of these prisms needs to be greater than the refractive index of the tempered glass 200, because light rays optically enter and exit the surface 210 of the tempered glass 200 through these prisms.

[0040] Furthermore, the exit angle when light is emitted from the tempered glass 200 to the light extraction member 30 is approximately equal to the critical angle determined by the difference in refractive index between the tempered glass 200 and the prism. To efficiently allow light to enter and exit the tempered glass 200, the critical angle needs to be 60±15°, and 60±5° is more preferable. Furthermore, it is desirable to select an angle such that the incident light and the exiting light pass through the inclined surface of each prism approximately perpendicularly.

[0041] For example, if the wavelength of the light source 10A is 589 nm, the inclination 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.

[0042] Furthermore, it is preferable that the refractive index ratio between two wavelengths of the prism that is the light extraction member 30 is the same as the refractive index ratio between 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, it is preferable that the refractive index ratio of the prism at 589 nm and 365 nm is the same as the refractive index ratio of the tempered glass 200. This is because the position of the boundary line described below can be made approximately the same when the light source 10A and the light source 10B are used.

[0043] Instead of prisms, other members having similar functions may be used as the light supplying member 20 and the light extracting member 30. The light supplying member 20 and the light extracting member 30 may be integrally constructed. To ensure stable optical contact, a liquid (which may be gel-like) with a refractive index between the refractive index of the light supplying member 20 and the light extracting member 30 and the refractive index of the tempered glass 200 may be filled between the refractive index of the light supplying member 20 and the light extracting member 30 and the refractive index of the tempered glass 200.

[0044] An imaging element 60 is disposed in the direction of the light emitted from the light extraction member 30, and a light conversion member 40 and a polarizing member 50 are inserted between the light extraction member 30 and the imaging element 60.

[0045] The light converting member 40 has a function of converting two types of light components contained in the light emitted through the light extracting member 30, vibrating parallel and perpendicular to the boundary surface between the tempered glass 200 and the light extracting member 30, into two types of bright line rows, two types of bright lines, and / or two types of boundary lines generated at a critical angle due to the refractive index difference between the tempered glass 200 and the light supplying member 20. As the light converting member 40, for example, a convex lens can be used, but other members having a similar function may also be used.

[0046] Furthermore, when a convex lens is used as the light converting member 40, it is desirable to use a combined lens (achromatic lens) having the same focal length for each wavelength of the light sources 10A and 10B.

[0047] A focal length of 100 mm to 300 mm is typically used. The focal length is related to the width of the bright line array that can be captured at one time by the imaging element 60; a short focal length allows a wide bright line array to be captured at one time, but makes it difficult to resolve and capture fine bright line arrays. The opposite is true for a long focal length; this focal length range is the optimal value required for measuring ordinary tempered glass.

[0048] Figure 2 shows the effect of using an achromatic lens. Figure 2(a) shows a photograph of the line train obtained by using a lens with chromatic aberration, optimally focused at 589 nm, and then moving the lens position at 365 nm. Figure 2(b) shows an image at 365 nm using a combined lens (achromatic lens) with the same focal length at both wavelengths, optimally focused at 589 nm.

[0049] In Figure 2(a), the image of the 365 nm emission line array, which has a focal length 4% smaller, is out of focus, making it difficult to accurately measure the emission line positions. In contrast, in Figure 2(b), the use of a combined lens (achromatic lens) reduces the focal length difference to 0.25%, resulting in an image that is in focus at both the 589 nm and 365 nm wavelengths, allowing accurate measurement of the emission line positions. In this way, it is preferable to keep the focal length difference between the two wavelengths to within ±3%, 2%, 1%, or 0.5%.

[0050] Returning to the explanation of Figure 1, the polarizing member 50 is a light separating means that has the function of selectively transmitting one of two types of light components that vibrate parallel and perpendicular to the interface between the tempered glass 200 and the light extraction member 30. As the polarizing member 50, for example, a rotatable polarizing plate or the like can be used, but other members having a similar function may also be used. Here, the light component that vibrates parallel to the interface between the tempered glass 200 and the light extraction member 30 is S-polarized light, and the light component that vibrates perpendicular to the interface is P-polarized light.

[0051] The boundary surface between the strengthened glass 200 and the light extraction member 30 is perpendicular to the exit surface of the light emitted to the outside of the strengthened glass 200 via the light extraction member 30. In other words, the light component that vibrates perpendicular to the exit surface of the light that has been emitted to the outside of the strengthened glass 200 via the light extraction member 30 is S-polarized light, and the light component that vibrates parallel to the exit surface is P-polarized light.

[0052] The imaging element 60 has a function of capturing images of two types of bright line rows, two types of bright lines, and / or two types of boundary lines converted by the light converting member 40. The imaging element 60 simultaneously or separately captures images of two types of bright line rows, two types of bright lines, and / or two types of boundary lines generated by light of multiple different wavelengths, while maintaining the relative positions of the tempered glass 200, the light extraction member 30, the light converting member 40, and the imaging element 60.

[0053] The imaging element 60 converts the light emitted from the light extraction member 30 and received via the light conversion member 40 and the polarization member 50 into an electrical signal. More specifically, the imaging element 60 can, for example, convert the received light into an electrical signal and output the luminance values ​​of each of a plurality of pixels that make up an image as image data to the calculation unit 70. As the imaging element 60, for example, an element such as a CCD (Charge Coupled Device) or a CMOS (Complementary Metal Oxide Semiconductor) can be used, but other elements having similar functions may also be used.

[0054] The calculation unit 70 has the function of taking in image data from the image sensor 60 and performing image processing and numerical calculations. The calculation unit 70 may be configured to have other functions (for example, a function to control the light intensity of the light source and exposure time). The calculation unit 70 can be configured to include, for example, a CPU (Central Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory), main memory, etc.

[0055] In this case, the various functions of the calculation unit 70 can be realized by reading a program recorded in a ROM or the like into main memory and executing it with a CPU. The CPU of the calculation unit 70 can read and store data from RAM as needed. However, part or all of the calculation unit 70 may be realized solely by hardware. Furthermore, the calculation unit 70 may be physically configured with multiple devices, etc. A personal computer, for example, can be used as the calculation unit 70.

[0056] In the stress measurement device 1, light ray L emitted from light source 10A or light source 10B is incident on the surface layer of tempered glass 200 through light supply member 20 and propagates within the surface layer. As light ray L propagates within the surface layer, modes are generated due to the optical waveguiding effect, and the light ray L travels along several predetermined paths and is extracted to the outside of the tempered glass 200 by light extraction member 30.

[0057] Then, the light is imaged as P-polarized and S-polarized bright lines for each mode on the image sensor 60 by the light conversion member 40 and the polarizing member 50. Image data of the P-polarized and S-polarized bright lines generated on the image sensor 60 for the number of modes is sent to the calculation unit 70. The calculation unit 70 calculates the positions of the P-polarized and S-polarized bright lines on the image sensor 60 from the image data sent from the image sensor 60.

[0058] Then, the light sources 10A and 10B of the two wavelengths are switched, and the positions of the P-polarized and S-polarized emission lines on the image sensor 60 at the wavelengths of the respective light sources are calculated from the image data at each wavelength. Furthermore, the relative positions of the strengthened glass 200, the light extraction member 30, the light conversion member 40, and the image sensor 60 are maintained between the images of the light sources 10A and 10B of the two wavelengths and the respective P-polarized and S-polarized light.

[0059] With this configuration, the stress measurement device 1 can calculate the refractive index distribution of each of the P-polarized light and the S-polarized light in the depth direction from the surface in the surface layer of the strengthened glass 200 based on the positions of the emission lines of the P-polarized light and the S-polarized light of the wavelengths of the light sources 10A and 10B. Furthermore, based on the difference between the calculated refractive index distributions of each of the P-polarized light and the S-polarized light and the photoelastic constant of the strengthened glass 200, the stress distribution in the depth direction from the surface in the surface layer of the strengthened glass 200 can be calculated.

[0060] Calculations such as calculation of bright line positions, refractive index distribution, and stress distribution from image data may be performed by first recording image data at two wavelengths and then using the recorded image data at the two wavelengths.

[0061] The measurement of the refractive index distribution and the measurement of the stress distribution in the stress measurement device 1 will be described in more detail below.

[0062] (Modes and emission lines) The trajectory and mode of a light ray when the light ray is incident on the surface layer of the tempered glass 200 will be described with reference to FIGS. 3 and 4. FIG.

[0063] In Fig. 3, tempered glass 200 has a refractive index distribution in the depth direction from surface 210. In Fig. 3, if the depth from surface 210 is x and the refractive index distribution in the depth direction is n(x), then the refractive index distribution n(x) in the depth direction will be, for example, like the curve shown in Fig. 4. That is, in tempered glass 200, the refractive index is high at surface 210 due to chemical strengthening or the like, and decreases with depth, until it becomes the same as the refractive index of the original glass at the depth where the compressive stress layer ends (the deepest part of the compressive stress layer), and remains constant (the refractive index of the original glass) at deeper portions.

[0064] As described above, the refractive index of the surface layer of the tempered glass 200 decreases as it travels toward the interior. Therefore, in Fig. 3, light ray L incident at a shallow angle with respect to the surface 210 (in the example of Fig. 3, the light ray L is incident via the light supply member 20, which has a refractive index higher than that of the tempered glass 200) gradually approaches parallel to the surface 210, and at the deepest point xt, the light ray is reversed from the depth direction toward the surface 210. Then, the light ray whose ray trajectory has been reversed travels toward the surface 210 in a shape similar to the shape of the ray trajectory from the point of incidence to the point of reversal, is at least partially reflected by the surface 210, and travels again into the tempered glass 200.

[0065] The light ray that has traveled back into the tempered glass 200 follows a trajectory of the same shape as the previous trajectory, turns around at depth xt, and returns to the surface 210, repeating this process as the light ray travels back and forth between the surface 210 and the deepest point xt. Since the light travels from the surface 210 through a limited space with a width xt, the light can only propagate as a discrete mode with finite values.

[0066] In other words, only a number of light rays along certain fixed paths can propagate through the surface layer of the tempered glass 200. This phenomenon is called the optical waveguiding effect, and is also the principle by which light rays travel within optical fibers. The mode of light propagating through the surface 210 due to the optical waveguiding effect and the trajectory of the light rays in that mode are determined by the refractive index distribution in the depth direction from the surface 210.

[0067] FIG. 5 is a diagram illustrating the ray trajectories of each mode when multiple modes exist. In the example of FIG. 5, three modes, mode 1, mode 2, and mode 3, are shown, but higher-order modes may also be included. In mode 1, which has the lowest order, the angle between the ray trajectory and surface 210 when the ray trajectory is reflected from surface 210 is the shallowest (the exit complementary angle is smallest). The deepest point of the ray trajectory differs for each mode, with the deepest point xt1 of mode 1 being the shallowest. As the order of the mode increases, the angle between the ray trajectory and surface 210 when the ray trajectory is reflected from surface 210 increases (the exit complementary angle increases). The deepest point xt2 of mode 2 is deeper than the deepest point xt1 of mode 1, and the deepest point xt3 of mode 3 is even deeper than the deepest point xt2 of mode 2.

[0068] Here, the incident angle of a light ray to a given surface is the angle between the incident light ray and the normal to the given surface. In contrast, the complementary angle of incidence of a light ray to a given surface is the angle between the incident light ray and the given surface. In other words, if the incident angle of a light ray to a given surface is θ, the complementary angle of incidence of the light ray to the given surface is π / 2-θ. The same applies to the relationship between the exit angle of a light ray to a given surface and the complementary angle of exit.

[0069] 5, the incident light is represented by a single ray, but the incident light has a certain degree of spread. Even with this spread, the complementary angle of the light emitted from surface 210 in the same mode is the same. Furthermore, since light other than the generated mode cancels out, only light corresponding to each mode is emitted from surface 210.

[0070] 1, the light supply member 20, the light extraction member 30, and the tempered glass 200 have the same shape in the depth direction. Therefore, the light condensed by the light conversion member 40 is focused on the imaging element 60, which is the focal plane of the light conversion member 40, and the light corresponding to the mode forms an image as a bright line in the depth direction.

[0071] Since the emission complementary angle differs for each mode, the emission lines are arranged in order for each mode, forming an emission line array, as shown in Fig. 6. Note that the emission line array is usually a row of bright lines, but when the light supply member 20 and the light extraction member 30 in Fig. 1 are in contact and integrated, direct light from the light source acts as reference light on the emitted light, and it may become a row of dark lines. However, whether it is a row of bright lines or a row of dark lines, the positions of the lines are exactly the same.

[0072] In this way, bright lines appear as bright or dark lines when a mode is established. Even if the interference color of a bright line changes depending on the brightness of the reference light, this has no effect on the calculation of the refractive index distribution and stress distribution according to this embodiment. Therefore, in this application, for convenience, both bright and dark lines are referred to as bright lines.

[0073] The complementary angle of emergence when a light ray that has propagated within the surface layer is refracted and emitted to the outside of the tempered glass 200 is equal to the refractive index of the tempered glass 200 at the deepest point of the ray's trajectory within the surface layer, i.e., equal to that of the critically refracted light when a medium having a refractive index equal to the effective refractive index nn is in contact with the light extraction member 30. The deepest point in each mode can also be interpreted as the point at which the light ray in that mode is totally reflected.

[0074] Here, the relationship between the difference Δn in the effective refractive index nn between certain modes and the distance ΔS between the emission lines is expressed by the following formula 1 (Equation 1) and formula 2 (Equation 2), where f is the focal length of the light conversion member 40, np is the refractive index of the light extraction member 30, and ng is the refractive index of the tempered glass 200.

[0075]

number

[0076]

number

[0077] (Position of bright lines on the image sensor) The position of the bright line on the image sensor 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. Fig. 7 is a diagram showing an example of the trajectory of light L from the light source between the strengthened glass and the prism. In Fig. 7, when the effective refractive index of a certain bright line is nr, the angle of the inclined surface of the prism is α, and the angle between the line (optical axis) connecting the center of the image sensor 60 and the point where the light exits the strengthened glass 200 and the perpendicular to the prism surface is β, the relationship shown in the following formula 3 (numerical formula 3) holds.

[0078]

number

[0079] (Positions of emission lines of different wavelengths) In this embodiment, two different wavelengths are used, but the position of the bright line on the imaging element differs for each wavelength. The position of the bright line at a certain wavelength is determined by the refractive index of the tempered glass, the rate of change in refractive index due to the ion concentration of the tempered glass, the difference in optical path difference due to different wavelengths, the difference in photoelastic constant, the refractive index of the prism, etc. Since these values ​​differ for different wavelengths, even if light from the light source is incident at the same angle of incidence, the ray trajectories and optical path differences are different, and therefore the conditions for establishing the mode are different, and the position at which the bright line occurs is different.

[0080] Figure 8 shows an example (part 1) of emission line sequences for two wavelengths. The upper part of Figure 8 shows an example when the light source wavelength is 589 nm, and the lower part of Figure 8 shows an example when the light source wavelength is 365 nm, both of which are P-polarized light. The dashed lines SF1 and SF2 at the left end of each line in Figure 8 represent virtual mode 0 at the surface, which is a position extrapolated from modes 1 and 2 to the surface. The dashed lines BP1 and BP2 at the right end of each line in Figure 8 represent the boundary position where the brightness changes suddenly, which is a boundary line created at the critical angle due to the difference in refractive index between the tempered glass 200 and the light supply member 20. The effective refractive index corresponding to this boundary position corresponds to the refractive index of the deep portion of the tempered glass that is not reached by tempering, and is equal to the refractive index of the glass before tempering, i.e., n. Note that when Li-containing AlSi-based glass is chemically tempered with NaNO3 and KNO3, n is equal to the refractive index n' of the glass at the K diffusion depth. n' may be determined by a separate experiment.

[0081] On the other hand, if we consider the case where the boundary line position where the effective refractive index of light source 10A is ng is within the imaging range of the image sensor, Equation 2 is determined by the ratio of np to ng, and Equation 3 also states, as mentioned above, that it is desirable to select an angle at the inclined surface of the prism so that the incident and exiting light passes through approximately perpendicularly, and under such conditions, the value of β in Equation 3 is also dominated by the ratio of np to nr, i.e., the ratio of np to ng. Therefore, if the wavelength of the light source is changed by switching from light source 10A to light source 10B, Equation 3 shows that the position of the boundary line will be approximately the same even for the wavelength of light source 10B, as long as 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.

[0082] However, as mentioned above, the refractive index of the prism must be greater than that of the tempered glass, and it is industrially difficult to select glass for the prism with the exact same refractive index ratio as the tempered glass. If the refractive index ratios of the two wavelengths are different, the boundary positions indicated by dashed lines BP1 and BP2 for light source 10A and light source 10B will be shifted, as shown in Figure 8. If this shift is large, the two wavelengths may not fall within the same angle of view.

[0083] Therefore, in order to include all of the emission line rows at the wavelengths of the two light sources on the screen of the image sensor 60 while keeping the relative positions of the tempered glass, prism, lens, and image sensor constant, the refractive index ratio of the tempered glass and prism must be equal to or less than a certain value. The refractive indices of the tempered glass and prism at the two wavelengths are nλ1 and nλ2, and the refractive index ratio between the two wavelengths is v, as shown in Equation 4 (Number 4).

[0084]

number

[0085]

number

[0086] Figure 9 shows examples of bright line trains captured by an imaging element, with Figure 9(a) being an example when formula 5 is not satisfied, and Figure 9(b) being an example when formula 5 is satisfied. As shown in Figure 9(a), when formula 5 is not satisfied, only a portion of the bright line train at one wavelength (589 nm in Figure 9(a)) is captured, making it impossible to analyze.

[0087] In such cases, the position of the image sensor is usually moved so as to approach angle β calculated by equation 3, as shown in Fig. 10. For example, by mechanically moving the lens and image sensor so that the angle changes from the solid arrow in Fig. 10 to the dashed arrow, it becomes possible to capture all of the bright line rows.

[0088] However, measuring the bright line position requires an accuracy of less than 1 μm, and moving the image sensor with that level of accuracy is extremely difficult. Therefore, it is preferable to select an appropriate image sensor width, lens focal length, prism refractive index, and refractive index ratio to capture the entire bright line array in an image at once. Furthermore, when capturing images using two wavelength light sources 10A and 10B while maintaining the relative positions of the tempered glass, prism, lens, and image sensor, it is preferable to use a combination lens (achromatic lens) with the same focal length at the two wavelengths. The effect of using an achromatic lens has been described with reference to Figure 2.

[0089] (Method of converting emission line positions into images with different wavelengths) Fig. 11 shows an example (part 2) of emission line trains at two wavelengths. Fig. 11 shows emission line trains at each wavelength for two light sources 10A and 10B, where the refractive index ratio between the prism and the tempered glass is approximately the same and the relative positions of the tempered glass, the prism as a light extraction member, the lens as a light conversion member, and the image sensor are maintained. In Fig. 11, the wavelength of light source 10A is 365 nm, and the wavelength of light source 10B is 589 nm.

[0090] As can be seen in Figure 11, the line array with a shorter wavelength of 365 nm has a larger number of lines and is denser. This is because the wavelength is shorter and the period of the interference conditions is shorter. The meanings of the dashed lines SF1 and SF2 and the dashed lines BP1 and BP2 are the same as in Figure 8.

[0091] In Figure 11, the boundary positions indicated by dashed lines BP1 and BP2 are the positions of the refractive index corresponding to the critical angle determined by the refractive index of the prism and the central part of the glass that is not tempered. In tempered glass, the refractive index distribution in the depth direction due to tempering becomes the refractive index of the central part of the tempered glass that is not tempered, which can also be understood as the maximum depth of tempering.

[0092] At different wavelengths, even for emission lines of the same mode, the effective refractive index and depth of the emission line are different, but the depth between the surface and the deepest position to which the strengthening has reached, i.e., the depth of the boundary position, is determined by the tempered glass and does not change depending on the wavelength.

[0093] That is, the depth of the effective refractive index of the virtual emission line of mode 0, which is 0 μm from the surface, is the same for both 365 nm and 589 nm from the surface and the boundary position. Therefore, to replace the position of the 589 nm emission line into the 365 nm emission line row, we can do the following:

[0094] That is, as shown in Figure 12, the emission line position of mode 0 at 589 nm (dashed line SF1) and the boundary emission line position (dashed line BP1) are aligned with the emission line position of mode 0 at 365 nm (dashed line SF2) and the boundary emission line position (dashed line BP2), and the emission line positions of modes other than mode 0 at 589 nm are superimposed on the position of the image of the 365 nm emission line sequence at the same ratio. Figure 13 shows the emission line sequence when the emission lines at 589 nm are fitted onto the image of the 365 nm emission line sequence.

[0095] On the other hand, the equation for the optical path difference that causes interference, which is the condition for each mode at two wavelengths, is expressed as Equation 6 (Number 6) based on Equation 8 explained below, where the optical path difference at 365 nm is L365, the number of modes is N, the optical path difference at 589 nm is L589, and the number of modes is N'.

[0096]

number

[0097]

number

[0098] Then, the extended mode number M of the emission line train in Figure 13 is 1, 1.32, 2, 2.95, 3, etc. from left to right. Table 1 shows the correspondence between the mode numbers at 365 nm and 589 nm, and the extended mode number M when the 589 nm emission line train is superimposed on the 365 nm emission line train.

[0099] [Table 1] (Calculation of refractive index distribution) In this embodiment, the refractive index distribution is calculated using the following equation 8 (numerical formula 8). In this embodiment, the refractive index distribution is calculated from emission lines of two wavelengths, but for ease of explanation, a calculation method from an emission line at a certain wavelength will be described here. Equation 8 was derived by the inventors based on the technical information and the like described in Non-Patent Document 1. Non-Patent Document 1 assumes that the refractive index distribution changes linearly, and approximates the path of light travel as a circular 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 under which a mode is established with an arbitrary refractive index distribution.

[0100] In Equation 3, θ is the complementary angle of emergence of a ray of light traveling in a straight line over a small distance dr, n0 is the refractive index of the tempered glass surface, Θ is the complementary angle of emergence of a ray of light incident on the tempered glass, λ is the wavelength of the ray of light incident on the tempered glass, and N is the order of the mode (for example, N = 1 for mode 1). Also, G1 is the point at which the ray of light enters the tempered glass, F2 is the deepest point (xt) at which the ray of light is inverted, and G2 is the point at which the ray of light inverted at F2 reaches the tempered glass again, and these terms differ for each mode. The first term on the left side is a term related to light propagating within the surface layer, and the second term on the left side is a term related to light propagating on the surface 210.

[0101]

number

[0102] 5, the refractive index of the surface layer at the deepest depths of each mode, xt1, xt2, xt3, i.e., the effective refractive index, is denoted by n1, n2, n3, etc. The refractive index change rates between the surface 210 and xt1, between xt1 and xt2, between xt2 and xt3, etc. are assumed to be linear, and the refractive index change rates are denoted by α1, α2, α3, etc.

[0103] The ray trajectory in a certain mode n passes through a portion shallower than the deepest point xtn of that mode, so if the refractive index distribution from the surface to xtn is determined, the ray trajectory in that mode n is uniquely determined. If xt for all modes is known, the refractive index distribution is uniquely determined, but from Equation 8, it is difficult to directly determine the refractive index distribution in one go, not only analytically but also numerically.

[0104] Therefore, first, α1, α2, xt1, and xt2 are calculated using mode 1 and mode 2, which pass through the part closest to the surface 210. Then, for mode 3, xt1 and xt2 are known and the only unknown parameter is xt3, so xt3 can be easily calculated. Similarly, by calculating xt4, xt5, etc. for modes 4, 5, etc., it is possible to calculate xtn at the deepest point corresponding to all modes. Then, the refractive index distribution in the depth direction from the surface 210 can be calculated.

[0105] FIG. 14 is a diagram illustrating an example of ray trajectories inside glass. A specific method for calculating the refractive index distribution will be described with reference to FIG. 14. First, the left side of Equation 8 is found using ray tracing. In FIG. 14, the x direction (vertical direction) is the depth direction of the tempered glass 200, and the y direction (horizontal direction) is the direction parallel to the surface 210 of the tempered glass 200. The refractive index at depth x is n(x). Note that H is the normal to the surface 210.

[0106] Here, let us consider a light ray L that is incident on the surface 210 from the light supply member 20 at a complementary angle of incidence Ψ, assuming that the refractive index of the light supply member 20 is 1.72. The coordinates of the incident point are (x0, y0). Note that x0=0. At this time, the light ray L that enters the tempered glass 200 is refracted at a complementary angle of emergence θ1 and travels forward. At this time, the Snell equation holds for Ψ and θ1.

[0107] Next, assume that the trajectory of light ray L inside the tempered glass 200 is a curve, but that it travels in a straight line for a small distance dr (the distance dr is preferably about 1 / 10 to 1 / 100 of the wavelength). In other words, assume that the light ray travels in a straight line the distance dr in the direction of the emission complementary angle θ1. In this case, the amount of movement in the x direction is dx1 = dr·sinθ1, and the amount of movement in the y direction is dy1 = dr·cosθ1. Also, the coordinates of the moved point are (x1, y1) = (dr·sinθ1, y0 + dr·cosθ1).

[0108] The refractive index at the coordinates of the start point of this partial ray trajectory (x0 = 0, y0) is n(0), and the refractive index at the coordinates of the end point (x1, y1) is n(x1). However, the refractive index at the start point is assumed to be constant within this ray trajectory, and changes to n(x1) at the end point. Then, the next ray trajectory follows Snell's law, changing its angle to an emergence complementary angle θ2. The light traveling at the emergence complementary angle θ2 travels in a straight line by dr, then changes direction to an emergence complementary angle θ3 (not shown) and travels on. This process is repeated to trace the ray trajectory to find the entire ray trajectory.

[0109] At this time, the first term on the left side of equation 8 is calculated each time dr advances. For example, in the area from coordinates (x0=0, y0) to coordinates (x1, y1), the first term is dr·cosθ1·n(0), which can be calculated easily. The calculations for other dr can be done in the same way. Then, by adding up the first terms calculated for each dr until the ray trajectory returns to the surface 210, all of the first terms on the left side of equation 8 can be calculated. At this time, the distance Σdy that this ray trajectory advances in the y direction can be determined. In equation 8, d G1G2 =Σdy, Θ=θ1, the second term on the left side of equation 8 can be found, and the entire left side of equation 8 can be found.

[0110] Next, a method for calculating the refractive index distribution will be described. First, as shown in Non-Patent Document 1, the refractive index of the surface 210 and the deepest point of mode 2 are determined from the positions of the emission lines of mode 1 and mode 2. This determines the values ​​of three points: the surface 210 (x=0), the deepest point of mode 1 (xt1), and the deepest point of mode 2 (xt2), as well as the refractive indices n0, n1, and n2 at those points. However, because the surface is an extrapolation of mode 1 and mode 2, these three points are straight lines.

[0111] Next, assuming that the deepest point xt3 in mode 3 is an appropriate value, the refractive index distribution up to xt3 can be defined, and the left side of equation 8 for this distribution can be calculated using the above calculation method. In other words, the left side of equation 8 can be calculated using xt3 as the only parameter, and the right side is determined by the order of the mode, which is 2.75λ for mode 3.

[0112] Then, by using xt3 as a parameter and using a nonlinear equation calculation method such as bisection or Newton's method, xt3 can be easily calculated. Once xt3 is calculated, xt4 can be found from the position of the emission line of the next mode 4, and by repeating the same calculation for all emission lines, the overall refractive index distribution can be calculated.

[0113] (Calculation of stress distribution) Because tempered glass has strong compressive stress within its plane, the refractive index of P-polarized light and the refractive index of S-polarized light differ by the amount of stress due to the photoelastic effect. In other words, when in-plane stress exists on surface 210 of tempered glass 200, the refractive index distribution differs between P-polarized light and S-polarized light, the way modes are generated differs, and the positions of the emission lines also differ.

[0114] Therefore, if the positions of the emission lines for P-polarized light and S-polarized light are known, the refractive index distributions for P-polarized light and S-polarized light can be calculated inversely. Based on the difference in the refractive index distributions for P-polarized light and S-polarized light and the photoelastic constant of tempered glass 200, the stress distribution σ(x) in the depth direction from surface 210 of tempered glass 200 can be calculated.

[0115] Specifically, the stress distribution can be calculated using the following equation (9): In equation (9), kc is the photoelastic constant, and Δn PS (x) is the difference between the refractive index distribution of P-polarized light and S-polarized light. The refractive index distribution of P-polarized light n P (x) and the refractive index distribution of S-polarized light n S Since (x) is obtained discretely, the stress distribution at any position can be obtained by linearly approximating the points or by calculating an approximate curve using multiple points.

[0116]

number

[0117] However, because the CT value and DOL value are calculated from the minute difference in refractive index between P-polarized light and S-polarized light, the difference in refractive index between P-polarized light and S-polarized light becomes small, particularly in areas where the change in refractive index is small (near the zero cross where the slope of the refractive index distribution becomes gentle), resulting in large measurement errors. Therefore, the CT value may be calculated using Equation 10 (Number 10) so that the value obtained by integrating the calculated stress distribution of the compressive stress layer in the depth direction of the tempered glass 200 balances with the tensile stress inside the tempered glass 200.

[0118] Here, CS(x) is the compressive stress value at position x in the depth direction of the tempered glass 200 shown in Fig. 14. For example, the integration range is set from the surface 210 to the center of the tempered glass 200, and the CT value can be determined so that the integration result is zero. In this case, the depth at which the stress becomes zero may be calculated as the DOL value.

[0119]

number

[0120] (Method of converting emission line positions into images with different wavelengths) The positions of the bright lines and boundary lines are measured to calculate the refractive index distribution and stress distribution. Bright lines have peaks or valleys in their brightness curves, so their positions can be measured with high precision. Meanwhile, the boundary line is located where the brightness is inclined. A common method for measuring the position of the boundary line from an image is to use the position of the maximum slope of the brightness curve as the boundary. However, due to factors such as the uniformity of the brightness of light sources 10A and 10B, the brightness gradient at the boundary line differs, and the boundary line position cannot always be measured with high reproducibility.

[0121] Furthermore, if the rightmost bright line happens to be close to the boundary, it is particularly difficult to measure the boundary position accurately. Figure 15 shows images of two types of bright line rows and their brightness curves. In Figure 15(a), the rightmost bright line (indicated by arrow BL1) is far from the boundary position, but in Figure 15(b), the rightmost bright line (indicated by arrow BL2) happens to be very close to the boundary position.

[0122] Comparing the brightness distributions of the two bright line rows shown in Figure 15, in Figure 15(a) the brightness at the boundary changes sharply, making it easy to measure the boundary position. However, in Figure 15(b), the bright line is adjacent to the boundary, so the brightness curve of the bright line and the brightness curve of the boundary overlap, making it difficult to accurately measure the boundary position.

[0123] In this embodiment, when combining two emission lines of one wavelength into an emission line row of either wavelength, the relative position of each emission line from the boundary is measured. However, as mentioned above, if the emission line positions of the two wavelengths, P polarization and S polarization, are shifted, the positional relationship of the emission lines of the two wavelengths will be shifted when combined, which will cause a large error when calculating the refractive index distribution or stress distribution from the combined emission line row.

[0124] When calculating the stress distribution from the surface of the tempered glass in the depth direction based on the positions of the two types of bright line rows in light of multiple different wavelengths, the positions of the two types of bright lines, and / or the positions of the two types of boundary lines, it is possible to refer to data previously measured on tempered glass with the same composition as the tempered glass to be measured.

[0125] For example, the line position is converted using only the boundary position of the converted and inserted glass, using a standard magnification measured in advance using tempered glass that has the same composition as the tempered glass to be measured but has been moderately tempered, and a boundary position difference calculated from the refractive index at two wavelengths of the tempered glass and the prism.Then, for the line sequence of the wavelength to be converted, the boundary position of the converted line sequence is calculated from the boundary position of the line sequence of the wavelength to be inserted based on the refractive index at two wavelengths of the prism and the tempered glass, and the converted line position is converted and inserted using this position as the boundary position of the converted line sequence.

[0126] This standard glass is preferably tempered to a certain degree and deep conditions, and is preferably not saturated so that the stress is nearly linear in the shallow portion where modes 1 and 2 occur.

[0127] (Example of standard magnification and boundary position difference measurement) Figure 16 shows standard magnifications and emission line sequences at 365 nm and 589 nm for standard tempered glass to measure the boundary position difference between wavelengths.

[0128] Figure 16 shows, from top to bottom, images of bright line sequences of 365 nm P-polarized light, 365 nm S-polarized light, 589 nm P-polarized light, and 589 nm S-polarized light, with the relative positions of the tempered glass, prism, lens, and image sensor all maintained.

[0129] The dashed lines SF (365 nm) and SF (589 nm) are the positions of the virtual mode 0 emission line on the surface, calculated from the respective mode 1 and mode 2 emission lines. This can be calculated using the method described in Non-Patent Document 1.

[0130] Next, the distances from mode 0 to the boundary for both P and S polarization at 365 nm and 589 nm are measured, and the ratio of these distances is calculated. Figure 16 shows the distance from virtual mode 0 to the boundary for S polarization, where d365 and d589 are the distances from virtual mode 0 to the boundary for S polarization at each wavelength. These ratios are then used as the magnifications riU and riL. The magnifications riU and riL are slightly different for P and S polarization. This difference is due to the photoelastic effect of the internal stress of the glass caused by tempering. The boundary position difference dre is calculated by measuring the difference in the position of the boundary between 365 nm and 589 nm for P and S polarization, and the average of the results for P and S polarization is used as the boundary position difference.

[0131] Furthermore, the magnification and boundary position difference for these standard tempered glasses can be measured with higher accuracy by measuring a plurality of standard tempered glasses and averaging the results.

[0132] (How to calculate the boundary position from one boundary position to another) In this embodiment, assuming that the relative positions of the prism, tempered glass, lens, and image sensor are constant, the remaining boundary positions are calculated based on one of the four boundary positions for two wavelengths, P polarization, and S polarization from the image, using the standard magnification and distance difference obtained by the above method.

[0133] Here, using the example of wavelengths of 365 nm and 589 nm above, we measure the boundary position of P-polarized light on the tempered glass to be measured. The position shifted from that boundary position by the boundary position difference dre calculated above is the boundary position of P-polarized light at 589 nm.

[0134] Furthermore, since the boundary position of S-polarized light is almost the same as that of P-polarized light, the boundary position of P-polarized light can also be used. Furthermore, accuracy can be improved by correcting the boundary position of S-polarized light by the CT value. The amount of correction can be estimated by measuring the CS and CT values ​​of the standard tempered glass mentioned above, and then using the ratio of the CS and CT values ​​to estimate the distance between the emission line position of S-polarized mode 1 and the hypothetical boundary position. Once the four boundary positions have been determined, the refractive index distribution and stress distribution can be calculated using the method described above.

[0135] (Method of measuring stress in the case of one emission line) Figure 17 shows the positions of the bright lines and boundary lines when there is one bright line at each wavelength of the light source. Although there is one bright line at each wavelength, it is inserted into the bright line image of a different wavelength using the same method as above. Then, the virtual bright line position on the surface is calculated from the positions of the two bright lines inserted into the bright line image of one wavelength.

[0136] When the wavelengths are 589 nm and 365 nm, if the 589 nm emission line is superimposed on the image of the 365 nm emission line, the mode numbers of these two emission lines are 1 and 1.32. Just as the position of the virtual mode 0 emission line was previously determined by extrapolation from modes 1 and 2 at a single wavelength, this time we can determine the virtual mode 0 from the emission lines of modes 1 and 1.32.

[0137] The virtual emission line position V on the surface can be extrapolated using Equation 11, where A is the emission line position closest to the surface and B is the next closest emission line position. kw is a constant determined by the two wavelengths, and for the combination of 365 nm and 589 nm, kw = 2.56.

[0138]

number

[0139]

number

[0140] First, in step S501, light of a first wavelength from the light source 10A is incident on a surface layer having a compressive stress layer of the tempered glass 200 via the light supply member 20 (first light supply step). Next, in step S502, the light of the first wavelength emitted by the light source 10A and propagated through the surface layer of the tempered glass 200 is emitted to the outside of the tempered glass 200 via the light extraction member 30 (first light extraction step).

[0141] Next, in step S503, two types of light components that are contained in the light of the first wavelength that has been emitted to the outside of the tempered glass 200 via the light extraction member 30 and that vibrate parallel and 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 types of bright line rows, two types of bright lines, and / or two types of boundary lines (first light conversion step). Note that the positions of the boundary lines differ between P-polarized light and S-polarized light, so the light is converted into two types of boundary lines.

[0142] Next, in step S504, the image sensor 60 captures two types of bright line rows, two types of bright lines, and / or two types of boundary lines at the first wavelength converted by the first optical conversion process (first image capturing process).

[0143] Next, in step S505, the position measurement means 71 of the calculation unit 70 measures the positions of the two types of bright line rows, the positions of the two types of bright lines, and / or the positions of the two types of boundary lines from the image of light from the light source 10A obtained by the image sensor 60 in the first imaging process (first position measurement process).

[0144] Next, in step S506, the light source is switched, and light of the second wavelength from the light source 10B is incident on 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 that has been propagated through the surface layer of the tempered glass 200 by the light source 10B is emitted to the outside of the tempered glass 200 (second light extraction step).

[0145] Next, in step S508, two types of light components that are contained in the light of the second wavelength that has been emitted to the outside of the tempered glass 200 via the light extraction member 30 and that vibrate parallel and 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 types of bright line rows, two types of bright lines, and / or two types of boundary lines (second light conversion step). Note that the positions of the boundary lines differ between P-polarized light and S-polarized light, so the light is converted into two types of boundary lines.

[0146] Next, in step S509, the image sensor 60 captures two types of bright line trains, two types of bright lines, and / or two types of boundary lines at the second wavelength converted by the second optical conversion process (second image capturing process).

[0147] Next, in step S510, the position measurement means 71 of the calculation unit 70 measures the positions of the two types of bright line rows, the positions of the two types of bright lines, and / or the positions of the two types of boundary lines from the image of light from the light source 10B obtained by the image sensor 60 in the second imaging process (second position measurement process).

[0148] Next, in step S511, the emission line sequence overlapping means 72 converts the emission line sequence of one wavelength at the positions of each of the two emission line sequences at the two wavelengths, inserts it into the other emission line sequence, and overlaps them (emission line sequence overlapping process).

[0149] Next, in step S512, the refractive index distribution calculation means 73 calculates the refractive index distribution from the surface of the strengthened glass 200 in the depth direction corresponding to each of the superimposed bright line sequences of the two types of light components (refractive index distribution calculation step).

[0150] Next, in step S513, the stress distribution calculation means 74 calculates the stress distribution from the surface of the tempered glass 200 in the depth direction based on the difference in refractive index distribution of the two types of light components and the photoelastic constant of the glass (stress distribution calculation process, etc.).

[0151] 19, the calculation unit 70 may include a CT value calculation means for calculating a CT value, a DOL value calculation means for calculating a DOL value, etc. In this case, the CT value and the DOL value can be calculated based on the stress distribution calculated by the stress distribution calculation means 74.

[0152] As described above, in the stress measurement device and stress measurement method according to this embodiment, the image sensor 60 simultaneously or separately captures two types of bright line trains, two types of bright lines, and / or two types of boundary lines using light of multiple different wavelengths while maintaining the relative positions of the strengthened glass 200, the light extraction member 30, the light conversion member 40, and the image sensor 60. The position measurement means 71 then measures the positions of the two types of bright line trains, the positions of the two types of bright lines, and / or the positions of the two types of boundary lines from each image using light of multiple different wavelengths obtained by the image sensor 60. Furthermore, the stress distribution calculation means 74 calculates the stress distribution from the surface of the strengthened glass 200 in the depth direction based on the positions of the two types of bright line trains, the positions of the two types of bright lines, and / or the positions of the two types of boundary lines using light of multiple different wavelengths measured by the position measurement means 71. This increases the effective number of bright lines, even for strengthened glass that has a very small number of bright lines, and in some cases has only one bright line, resulting in improved measurement accuracy of the stress distribution near the surface of the strengthened glass.

[0153] [Table 2] Table 2 is a table explaining the refractive index ratio of a suitable prism in this embodiment, and uses measurements of DT glass (Dragontrail), a tempered glass manufactured by AGC, as an example.

[0154] The refractive index of tempered glass (DT glass) is 1.53 at 365 nm and 1.509 at 589 nm, resulting in a refractive index ratio (365 nm / 589 nm) of 1.0139. Furthermore, the maximum tempering condition for this tempered glass—that is, the change in refractive index when almost all of the Na ions in the glass are replaced with K ions—i.e., the refractive index range of the emission line—is approximately 0.01 at both 365 nm and 589 nm. Therefore, the refractive index range (lower limit to upper limit of the emission line range) required for imaging is 1.53 to 1.54 at 365 nm and 1.509 to 1.519 at 589 nm. Furthermore, the left side of Equation 5 is 0.0056.

[0155] The stress measurement device used had a focal length of 166 mm and the width of the imaging area of ​​the image sensor was 3.45 μm (1 pixel size) × 1800 pixels = 6.210 mm. These are specifications commonly used in conventional stress measurement devices for tempered glass that use guided light.

[0156] Example 1 is an example where the refractive index ratio of the tempered glass and the prism is inappropriate and does not satisfy formula 5. In Example 1, the prism used is the S-LAL10 manufactured by Ohara, which has been widely used up until now.

[0157] When using the prism in Example 1, even if the measurable refractive index range is such that the 365 nm emission line train can be captured, it is 1.53 to 1.5484 at 365 nm and 1.4988 to 1.5169 at 589 nm according to equations 1, 2, and 3. Therefore, it is not possible to capture the required refractive index range at 589 nm. Also, the difference in refractive index ratio is 0.0070, which does not satisfy equation 5.

[0158] On the other hand, in Example 2, an Ohara S-LAL18 prism is used. The refractive index range for the glass material of the prism in Example 2 that can measure 589 nm is 1.5014 to 1.5194, so imaging is possible across the required refractive index range. In addition, the difference in refractive index ratio is 0.0052, which satisfies Equation 5.

[0159] Figure 20 shows photographs of the bright line arrays of DT glass that were nearly fully tempered under the conditions of Examples 1 and 2. Figure 20(a) is a photograph of Example 1, and Figure 20(b) is a photograph of Example 2.

[0160] As shown in Figure 20(b), in Example 2, the 365 nm and 589 nm emission line trains are all captured. In contrast, as shown in Figure 20(a), in Example 1, only about half of the 589 nm emission line train is captured. Note that the effect of the present invention is greater when the number of emission lines is small, but to make the shift in the emission line train easier to see, Figure 20 shows a photograph of a sample with a large number of emission lines.

[0161] As described above, in the stress measuring device and stress measuring method according to this embodiment, images are captured using light of a plurality of different wavelengths while maintaining the relative positions of the tempered glass 200, the light extraction member 30, the light conversion member 40, and the image sensor 60. Then, the stress distribution in the depth direction from the surface of the tempered glass 200 is calculated based on each image captured using light of a plurality of different wavelengths, thereby improving the measurement accuracy of the stress distribution near the surface of the tempered glass even when the number of emission lines is very small.

[0162] Furthermore, it is preferable to satisfy Expression 5 as in Example 2, which makes it possible to realize an even better stress measurement device and stress measurement method. That is, under any strengthening conditions, all of the emission line trains at two wavelengths can be captured with the optical system fixed, and highly accurate stress measurement becomes possible from the emission line trains at two wavelengths.

[0163] According to the stress measurement method described in the first embodiment, it is possible to calculate stress even in tempered glass having a CS value of 400 MPa or more, or in tempered glass having a DOL value of 3 μm or less observed with guided light, for example.

[0164] [Table 3] Table 3 shows the evaluation results of Na-containing AlSi-based glasses (Examples 3, 4, and 6) and Li-containing AlSi-based glasses (Examples 5 and 7). Figure 21 shows photographs of the bright line trains obtained in Examples 3 and 6, with Figure 21(a) being a photograph of Example 3 and Figure 21(b) being a photograph of Example 6.

[0165] The Na-containing AlSi-based glass was evaluated after immersion in 100% KNO3 molten salt at 380°C for 15 minutes and washing, and after immersion in 100% KNO3 molten salt at 380°C for 3 minutes and washing. The Li-containing AlSi-based glass was evaluated after immersion in 100% KNO3 molten salt at 400°C for 60 minutes, cooling and washing, and then immersion in 100% KNO3 molten salt at 380°C for 10 minutes, cooling and washing.

[0166] Examples 3 to 5 were evaluated using the method described in Patent Document 2 (hereinafter referred to as the conventional method), while Examples 6 and 7 were evaluated using the method described in the first embodiment (hereinafter referred to as the method of the present application). As a result, Example 3 could be evaluated using the conventional method, but Examples 4 and 5 could not be evaluated using the conventional method due to the insufficient number of P-polarized and S-polarized emission lines. On the other hand, the present method can evaluate even with a minimum number of emission lines of one, so in Examples 6 and 7, it was possible to derive the surface compressive stress value (CS value) and the depth of the compression layer (DOL) due to potassium exchange caused by substituting Na for K. As a result, it became possible to control the quality of glass, which could not be evaluated using the conventional method.

[0167] The dotted line BP1 is confirmed for P-polarized light and S-polarized light, and the refractive index difference is Δn PS (DOL), there is a correlation with the stress σ(DOL) at the depth DOL of the compressive stress layer ion-exchanged with potassium, and this stress can be calculated using equation (9). However, if the lithium contained in the glass is exchanged with sodium, σ(DOL) = f(Δn PS Similarly, σ(DOL) can be derived from the dashed line BP2.

[0168] By using the average value of the two σ(DOL) values ​​obtained from the dashed lines BP1 and BP2, a highly accurate σ(DOL) value can be used.

[0169] Furthermore, when the lithium contained in the glass is exchanged for sodium, the stress distribution σ(x) due to the sodium ions correlates with σ(DOL). Therefore, by using the average value or difference of the two σ(DOL), it is possible to predict the stress distribution σ(x) due to the sodium ions with high accuracy.

[0170] Second Embodiment The second embodiment will show an example of a stress measuring device in which the form of the light source is different from that of the first embodiment. Note that in the second embodiment, the description of the same components as those of the embodiments already described may be omitted.

[0171] Fig. 22 is a diagram illustrating a stress measurement apparatus according to the second embodiment. As shown in Fig. 22, in the stress measurement apparatus 2, a light source 10C has a function of emitting light of two different wavelengths. The light of the two different wavelengths can be electrically irradiated simultaneously or separately.

[0172] 23 is a diagram illustrating a light source of the stress measuring device according to the second embodiment. The light source 10C includes a plurality of light-emitting elements arranged adjacent to each other and emitting light of different wavelengths. Specifically, LED chips 101A and 101B capable of emitting light of different wavelengths are mounted adjacent to each other on a substrate 103 as the light-emitting elements. The shorter the distance between the LED chip 101A and the LED chip 101B, the better, but it is about 1 mm in view of the size of the chips.

[0173] As shown in FIG. 24, for example, a condenser lens 104 is arranged after the LED chips 101A and 101B, and a two-wavelength band-pass filter 105 is arranged after that.

[0174] As such, the form of the light source is not particularly limited, and may be any form as long as it can generate light of different wavelengths.

[0175] Third Embodiment The third embodiment shows an example of a stress measuring device having a different form of light source from that of the second embodiment. Note that in the third embodiment, the description of the same components as those of the already described embodiments may be omitted.

[0176] 25 is a diagram illustrating a stress measurement apparatus according to a third embodiment. In addition to the configuration of the second embodiment, the stress measurement apparatus 3 according to the third embodiment has a segmented polarizing filter 111 and a segmented band-pass filter 112 in front of the image sensor 60. This makes it possible to simultaneously acquire bright line images of P-polarized light and S-polarized light of two wavelengths in one shot. Unlike the second embodiment, a band-pass filter need not be provided in the rear of the light source 10C.

[0177] Fig. 26 is a diagram illustrating a segmented polarizing filter 111. Polarizing filter 111 shown in Fig. 26 is a light separating means having a region that transmits the light component vibrating parallel to the boundary surface of two types of light components, and a region that transmits the light component vibrating perpendicular to the boundary surface, and is disposed between image sensor 60 and bandpass filter 112. Specifically, polarizing filter 111 is divided at the center line into horizontal polarizing plate 111a, whose polarization direction is horizontal, and vertical polarizing plate 111b, whose polarization direction is vertical. In Fig. 26, the arrows indicate the polarization directions.

[0178] Fig. 27 is a diagram illustrating a segmented bandpass filter 112. The bandpass filter 112 shown in Fig. 27 is a light separation means for transmitting one or the other of two wavelengths emitted from a light source and for increasing monochromaticity, and is segmented into four regions 112a to 112d. The bandpass filter 112 has regions 112a and 112c that transmit only one wavelength λa of light from a light source with multiple wavelengths, and regions 112b and 112d that transmit only the other wavelength λb.

[0179] Regions 112a and 112b correspond to the horizontal polarizer 111a, and regions 112c and 112d correspond to the vertical polarizer 111b. That is, the light of one wavelength λa that has passed through region 112a of the bandpass filter 112 and the light of the other wavelength λb that has passed through region 112b of the bandpass filter 112 are incident on the horizontal polarizer 111a. Also, the light of one wavelength λa that has passed through region 112c of the bandpass filter 112 and the light of the other wavelength λb that has passed through region 112d of the bandpass filter 112 are incident on the vertical polarizer 111b.

[0180] In this way, by including the polarizing filter 111 and the bandpass filter 112, the stress measuring device 3 can capture bright line images of two wavelengths, P polarized light and S polarized light, in one image capture.

[0181] Although the preferred embodiments have been described in detail above, the present invention is not limited to the above-described embodiments, and various modifications and substitutions can be made to the above-described embodiments without departing from the scope of the claims. [Explanation of symbols]

[0182] 1, 2, 3 Stress measurement device 10A, 10B, 10C light source 15 Light introduction member 20 Light supply member 30 Light extraction member 40 Light conversion material 50 Polarizing element 60 image sensor 70 Arithmetic section 71 Position measuring means 72 Method for overlapping emission lines 73 Refractive index distribution calculation means 74 Stress distribution calculation method 101A, 101B LED chips 103 Substrate 104 Condenser Lens 105, 112 Bandpass filters 111 Polarizing Filter 111a Horizontal polarizer 111b Vertical polarizer 112a, 112b, 112c, 112d areas 200 tempered glass 210 Surface

Claims

1. a light source having a function of emitting light of a plurality of different wavelengths; a light supply member that allows light from the light source to enter a surface layer of the tempered glass having a compressive stress layer; a light extraction member that outputs the light that has propagated within the surface layer to the outside of the tempered glass; a light conversion member that converts two types of light components that are included in the light emitted through the light extraction member and vibrate parallel and perpendicular to the boundary surface between the strengthened glass and the light extraction member into two types of bright line rows, two types of bright lines, and / or two types of boundary lines that occur at a critical angle due to a refractive index difference between the strengthened glass and the light supply member; an imaging element that images the two types of bright line rows, the two types of bright lines, and / or the two types of boundary lines; a position measuring means for measuring the positions of the two types of bright line rows, the positions of the two types of bright lines, and / or the positions of the two types of boundary lines from each of the images obtained by the imaging element using light of the plurality of different wavelengths, the imaging element simultaneously or separately images the two types of bright line rows, the two types of bright lines, and / or the two types of boundary lines generated by the light of the plurality of different wavelengths while maintaining a positional relationship between the strengthened glass, the light extraction member, the light conversion member, and the imaging element; calculating stress in a depth direction from the surface of the strengthened glass by synthesizing the plurality of bright line sequences of different wavelengths based on positions of the two types of bright line sequences, positions of the two types of bright lines, and / or positions of the two types of boundary lines in the plurality of different wavelengths measured by the position measuring means; The stress measurement device for tempered glass, characterized in that synthesizing the plurality of emission line trains of different wavelengths includes expressing a mode of one wavelength as an extended mode number in which the mode number of the other wavelength is a real number.

2. 2. The apparatus for measuring stress in tempered glass according to claim 1, wherein the formula 5 is satisfied for at least one wavelength among the plurality of different wavelengths. [Equation 5] In Equation 5, k1 is a parameter, f is the focal length of the light conversion member, np is the refractive index of the light extraction member, ng is the refractive index of the tempered glass, W is the width of the image sensor, S is the width of the bright line row, vp is the refractive index ratio of the light extraction member at a plurality of different wavelengths, and vg is the refractive index ratio of the tempered glass at a plurality of different wavelengths.

3. a light source having a function of emitting light of a plurality of different wavelengths; a light supply member that allows light from the light source to enter a surface layer of the tempered glass having a compressive stress layer; a light extraction member that outputs the light that has propagated within the surface layer to the outside of the tempered glass; a light conversion member that converts two types of light components that are included in the light emitted through the light extraction member and vibrate parallel and perpendicular to the boundary surface between the strengthened glass and the light extraction member into two types of bright line rows, two types of bright lines, and / or two types of boundary lines that occur at a critical angle due to a refractive index difference between the strengthened glass and the light supply member; an imaging element that images the two types of bright line rows, the two types of bright lines, and / or the two types of boundary lines; a position measuring means for measuring the positions of the two types of bright line rows, the positions of the two types of bright lines, and / or the positions of the two types of boundary lines from each of the images obtained by the imaging element using light of the plurality of different wavelengths, the imaging element simultaneously or separately images the two types of bright line rows, the two types of bright lines, and / or the two types of boundary lines generated by the light of the plurality of different wavelengths while maintaining a positional relationship between the strengthened glass, the light extraction member, the light conversion member, and the imaging element; calculating stress from a surface of the tempered glass in a depth direction based on positions of the two types of bright line rows, positions of the two types of bright lines, and / or positions of the two types of boundary lines in the light of the plurality of different wavelengths measured by the position measuring means; The apparatus for measuring stress in tempered glass, wherein Equation 5 is satisfied at at least one wavelength among the plurality of different wavelengths. [Equation 5] In Equation 5, k1 is a parameter, f is the focal length of the light conversion member, np is the refractive index of the light extraction member, ng is the refractive index of the tempered glass, W is the width of the image sensor, S is the width of the bright line row, vp is the refractive index ratio of the light extraction member at a plurality of different wavelengths, and vg is the refractive index ratio of the tempered glass at a plurality of different wavelengths.

4. 4. The apparatus for measuring stress in strengthened glass according to claim 1, wherein the light converting member is a combination lens having a difference in focal length of ±3% or less at the plurality of different wavelengths.

5. 5. The apparatus for measuring stress in tempered glass according to claim 1, wherein the wavelength of one of the light sources is 1.5 to 2.5 times the wavelength of the other light source.

6. 6. The stress measuring device for tempered glass according to claim 1, wherein when calculating the stress distribution from the surface of the tempered glass in the depth direction based on the positions of the two types of bright line rows in the light of the plurality of different wavelengths, the positions of the two types of bright lines, and / or the positions of the two types of boundary lines, reference is made in advance to data measured on tempered glass having the same composition as the tempered glass to be measured.

7. 7. The apparatus for measuring stress in tempered glass according to claim 1, wherein the light source includes a plurality of light-emitting elements arranged adjacent to each other and emitting light of different wavelengths.

8. 8. The stress measuring device for tempered glass according to claim 1, further comprising a first light separating means provided in front of the imaging element, the first light separating means having a region that transmits only one wavelength of the light from the light sources of the plurality of different wavelengths and a region that transmits only the other wavelength.

9. 9. The stress measuring device for tempered glass according to claim 8, further comprising: a second light separating means between the imaging element and the first light separating means, the second light separating means having a region that transmits a light component of the two types of light components that vibrates parallel to the boundary surface and a region that transmits a light component that vibrates perpendicular to the boundary surface.

10. a first light supplying step of causing light of a first wavelength to enter a surface layer of the tempered glass, the surface layer having a compressive stress layer, via a light supplying member; a first light extraction step of emitting the light of the first wavelength that has propagated through the surface layer to the outside of the strengthened glass via a light extraction member; a first light conversion step of converting, by a light conversion member, two types of light components that are included in the light of the first wavelength emitted to the outside of the tempered glass and vibrate parallel and perpendicular to the boundary surface between the tempered glass and the light extraction member, into two types of bright line rows, two types of bright lines, and / or two types of boundary lines that occur at a critical angle due to a refractive index difference between the tempered glass and the light supply member; a first imaging step of imaging the two types of bright line sequences, the two types of bright lines, and / or the two types of boundary lines by the first wavelength with an imaging element; a first position measuring step of measuring positions of the two types of bright line rows, positions of the two types of bright lines, and / or positions of the two types of boundary lines from the image using light of the first wavelength obtained in the first imaging step; a second light supplying step of causing light of a second wavelength to enter the surface layer through the light supplying member; a second light extraction step of emitting the light of the second wavelength that has propagated through the surface layer to the outside of the strengthened glass via the light extraction member; a second light conversion step of converting two types of light components, which are included in the light of the second wavelength emitted to the outside of the tempered glass and vibrate parallel and perpendicular to the boundary surface between the tempered glass and the light extraction member, into the two types of bright line rows, the two types of bright lines, and / or the two types of boundary lines; a second imaging step of imaging the two types of bright line rows, the two types of bright lines, and / or the two types of boundary lines by the second wavelength with the imaging element; a second position measuring step of measuring positions of the two types of bright line rows, positions of the two types of bright lines, and / or positions of the two types of boundary lines from an image using light of the second wavelength obtained in the second imaging step, In the first and second imaging steps, the two types of bright line rows, the two types of bright lines, and / or the two types of boundary lines are simultaneously or separately imaged by light of a plurality of different wavelengths while maintaining the relative positions of the strengthened glass, the light extraction member, the light conversion member, and the imaging element; calculating stress in a depth direction from the surface of the strengthened glass by synthesizing the plurality of bright line sequences of different wavelengths based on positions of the two types of bright line sequences, positions of the two types of bright lines, and / or positions of the two types of boundary lines in the plurality of different wavelengths measured in the first and second position measuring steps; A method for measuring stress in tempered glass, characterized in that synthesizing the plurality of emission line trains of different wavelengths includes expressing a mode of one wavelength as an extended mode number in which the mode number of the other wavelength is a real number.

11. 11. The stress measuring method for tempered glass according to claim 10, wherein, regardless of whether the light of the first wavelength or the light of the second wavelength is used, the stress in the depth direction from the surface of the tempered glass is calculated when a minimum number of emission lines observed by the two types of light components is one.

12. The method for measuring stress in strengthened glass according to claim 11, wherein either the first wavelength or the second wavelength is 400 nm or less.

Images