Reinforced glass stress measurement device, and reinforced glass stress measurement method

Abstract

To boost detection accuracy of a surface position of reinforced glass in a reinforced glass stress measurement device.SOLUTION: A reinforced glass stress measurement device has: a light feed member that makes laser light having a polarization phase difference varied by a polarization phase difference variable member incident into reinforced glass serving as a measured body; a liquid that is disposed in between the light feed member and the reinforced glass; a light conversion member that image-forms scattered light of the laser light incident into the reinforced glass; an image-capturing element that image-captures the scattered light image-formed on the light conversion member at a prescribed time interval a plurality of times to acquire a plurality of images; and a computation unit that measures a cyclic change in luminance of the scattered light, using the plurality of images, calculates a change in phase of the luminance change, and calculates a stress distribution in a depth direction from a surface of the reinforced glass on the basis of the phase change, in which the plurality of images includes a plurality of position detection images that image-captures scattered light generated inside the liquid, and scattered light generated inside the reinforced glass on the same screen and at the same time, and the computation unit is configured to detect the position of the reinforced glass on the basis of the plurality of position detection images.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Various stress measurement devices that measure stress in a measurement object nondestructively are known. One example is a stress measurement device that includes a polarization phase difference variable member that varies the polarization phase difference of laser light with respect to the wavelength of the laser light, an imaging element that captures images of scattered light emitted when the laser light, with the polarization phase difference varied, is incident on tempered glass multiple times at predetermined time intervals to obtain multiple images, and a calculation unit that measures periodic brightness changes in the scattered light using the multiple images, calculates a phase change of the brightness change, and calculates a stress distribution in the depth direction from the surface of the tempered glass based on the phase change (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2018 / 056121 Summary of the Invention [Problem to be solved by the invention]

[0004] The stress of chemically strengthened glass is distributed in a layer approximately 10 to several hundred microns deep from the surface, with stress varying significantly with depth, particularly in the several tens of microns near the surface. Therefore, measuring the stress distribution requires high spatial resolution in the depth direction, with a depth accuracy of approximately ±1 micron. To achieve a depth accuracy of approximately ±1 micron, the detection of the surface position of the strengthened glass must also be performed with an accuracy equal to or greater than the depth accuracy.

[0005] However, conventional stress measurement devices detect the position of the tempered glass surface based on mechanical positional relationships, and as a result, the position of the tempered glass surface can deviate from the correct position by several μm to several tens of μm due to factors such as temperature changes in the environment in which the stress measurement device is used or creaking of the stress measurement device.

[0006] The present invention has been made in view of the above points, and has an object to improve the detection accuracy of the position of the surface of tempered glass in a device for measuring stress on tempered glass. [Means for solving the problem]

[0007] the scattered light from the laser beam passing through the light supply member and the liquid and incident on the tempered glass; an image sensor that captures images of the scattered light formed on the light conversion member multiple times at predetermined time intervals to obtain multiple images; and a calculation unit that measures periodic luminance changes in the scattered light using the multiple images, calculates a phase change of the luminance change, and calculates a stress distribution in the depth direction from the surface of the tempered glass based on the phase change, wherein the multiple images include multiple position detection images obtained by simultaneously capturing the scattered light generated in the liquid and the scattered light generated in the tempered glass on the same screen, and the calculation unit detects the position of the surface of the tempered glass based on the multiple position detection images. [Effects of the Invention]

[0008] According to the disclosed technology, it is possible to improve the detection accuracy of the position of the surface of tempered glass in a tempered glass stress measuring device. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram illustrating a stress measuring device according to a first embodiment. [Figure 2] 2 is a view of the stress measuring device according to the first embodiment as viewed from the H direction in FIG. 1. [Figure 3] 10 is a diagram illustrating an example of the relationship between the voltage applied to a liquid crystal element and the polarization phase difference. FIG. [Figure 4] FIG. 10 is a diagram illustrating an example of a circuit that generates a drive voltage to a liquid crystal element such that the polarization phase difference changes linearly with time. [Figure 5] 1 is a diagram illustrating an example of a scattered light image at a certain moment of laser light L formed on an imaging element. [Figure 6] 6 is a diagram illustrating an example of the change over time in scattered light intensity at points B and C in FIG. 5. FIG. [Figure 7] FIG. 10 is a diagram illustrating an example of the phase of the scattered light change depending on the glass depth. [Figure 8] FIG. 8 is a diagram illustrating an example of stress distribution calculated from Equation 1 based on the phase data of the change in scattered light in FIG. 7. [Figure 9] 10A and 10B are diagrams illustrating actual scattered light images at different times t1 and t2. [Figure 10] 10 is a diagram showing an example of an undesirable design of a surface 250 through which laser light L travels in tempered glass. FIG. [Figure 11] 1 is a diagram showing a preferred design example of a surface 250 through which laser light L travels in tempered glass. [Figure 12] 1A and 1B are diagrams illustrating laser light reflected on a surface of strengthened glass. [Figure 13] FIG. 2 is a schematic diagram of a position detection image. [Figure 14] FIG. 2 is a diagram illustrating an example of functional blocks of a calculation unit 70 of the stress measurement device 1. [Figure 15] 1 is a flowchart illustrating an evaluation method using the stress measuring device 1. [Figure 16] 10 is an example of an image for position detection. [Figure 17] FIG. 1 is a diagram (part 1) showing a change in the phase difference of laser light. [Figure 18] FIG. 2 is a diagram (part 2) showing a change in the phase difference of laser light. [Figure 19] FIG. 10 is a diagram showing changes in luminance of laser light. [Figure 20] FIG. 10 is a diagram showing a change in the trajectory of a laser beam. DETAILED DESCRIPTION OF THE INVENTION

[0010] 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.

[0011] First Embodiment (Stress measurement device) Fig. 1 is a diagram illustrating a stress measuring device according to a first embodiment. As shown in Fig. 1, the stress measuring device 1 includes a laser light source 10, a polarizing member 20, a polarization phase difference variable member 30, a light supply member 40, a light converting member 50, an image pickup element 60, a calculation unit 70, a light wavelength selecting member 80, and a liquid 90.

[0012] The stress measuring device 1 varies the polarization phase difference of laser light by, for example, one or more wavelengths relative to the wavelength of the laser light, and captures scattered light emitted when the laser light with the varied polarization phase difference is incident on tempered glass multiple times at predetermined time intervals to obtain multiple images.The device then measures periodic luminance changes of the scattered light using the multiple obtained images, calculates phase changes of the luminance changes, and calculates stress distribution based on the phase changes.This will be described in detail below.

[0013] 1, the object to be measured is a tempered glass 200. The tempered glass 200 is glass that has been subjected to a tempering process, such as chemical tempering or air-cooling tempering.

[0014] The laser light source 10 is arranged so that laser light L is incident from the light supply member 40 onto the surface layer of the tempered glass 200, and a polarization phase difference variable member 30 is inserted between the laser light source 10 and the light supply member 40.

[0015] The laser light source 10 may be, for example, a semiconductor laser, a helium-neon laser, or an argon laser. Semiconductor lasers are usually polarized, and semiconductor lasers with wavelengths such as 405 nm, 520 nm, 630 nm, and 850 nm are in practical use. The shorter the wavelength of the laser light, the more the beam diameter can be narrowed and the higher the spatial resolution can be. Also, the shorter the wavelength of the laser light, the smaller the laser speckle noise tends to be, which is preferable. Note that the laser light must pass through the object to be measured.

[0016] In order to increase the resolution in the depth direction of the tempered glass 200, it is preferable that the position of the minimum beam diameter of the laser light is within the ion exchange layer of the tempered glass 200, and that the minimum beam diameter is 20 μm or less. It is even more preferable that the position of the minimum beam diameter of the laser light is on the surface 210 of the tempered glass 200. Note that since the beam diameter of the laser light determines the resolution in the depth direction, the beam diameter must be set to be equal to or less than the required resolution in the depth direction. Here, the beam diameter is defined as 1 / e when the brightness at the center of the beam is at its maximum. 2 When the beam shape is elliptical or sheet-shaped, the beam diameter refers to the minimum width. In this case, however, the minimum width of the beam diameter must be directed in the direction of the glass depth.

[0017] Since the cross-sectional shape of the beam emitted from a semiconductor laser is usually elliptical, shaping it into a circle using a beam shaping member can increase the spatial resolution and improve measurement accuracy. Also, although the power distribution within the beam shape of the beam emitted from a semiconductor laser is a Gaussian distribution, measurement accuracy can also be improved by shaping it into a constant distribution within the beam shape, such as a top-hat distribution, using a power distribution shaping member.

[0018] The beam shaping member and the output distribution shaping member are inserted, for example, between the laser light source 10 and the polarization phase difference variable member 30. Examples of the beam shaping member include a cylindrical lens, an anamorphic prism, and a diaphragm. Also, examples of the output distribution shaping member include an aspherical lens and a DOE (Diffractive Optical Element).

[0019] The polarizing member 20 is inserted between the laser light source 10 and the polarization phase difference variable member 30 as necessary. Specifically, when the laser light L emitted from the laser light source 10 is not polarized, the polarizing member 20 is inserted between the laser light source 10 and the polarization phase difference variable member 30. When the laser light L emitted from the laser light source 10 is polarized, the polarizing member 20 may or may not be inserted. Furthermore, the laser light source 10 and the polarizing member 20 are installed so that the polarization plane of the laser light L is at 45° with respect to the surface 210 of the tempered glass 200. As the polarizing member 20, for example, a polarizing plate fixed in a predetermined polarization direction can be used, but other members having a similar function may also be used.

[0020] The light supplying member 40 is placed in optical contact with the surface 210 of the tempered glass 200, which is the object to be measured, via the liquid 90. The light supplying member 40 has a function of making the light from the laser light source 10 incident on the tempered glass 200. For example, a prism made of optical glass can be used as the light supplying member 40. In this case, since the light beam optically enters the surface 210 of the tempered glass 200 through the prism, the refractive index of the prism needs to be approximately the same as the refractive index of the tempered glass 200 (within ±0.2).

[0021] The liquid 90 is disposed between the light supplying member 40 and the tempered glass 200. In the example of FIG. 1, a depression 40x is provided on the surface of the light supplying member 40, and the depression 40x is filled with the liquid 90. The depression 40x can be provided, for example, by polishing or etching the surface of the light supplying member 40. The bottom of the depression 40x does not need to be flat. The depression 40x can be, for example, spherical, similar to a concave lens.

[0022] Since the refractive index of the tempered glass 200 varies slightly depending on the type of tempered glass, in order to set the refractive index of the light supply member 40 to an "appropriate refractive index," it is necessary to replace the light supply member 40 for each type of tempered glass. However, since this replacement work is inefficient, by sandwiching a liquid 90 having an "appropriate refractive index" between the light supply member 40 and the tempered glass 200, the laser light L can be efficiently incident into the tempered glass 200. The "appropriate refractive index" will be described later.

[0023] As the liquid 90, for example, a mixture of 1-bromonaphthalene (n=1.64) and xylene (n=1.50) can be used. As the liquid 90, a mixture of multiple silicone oils with different structures can also be used. For example, the refractive index of dimethyl silicone oil (n=1.38 to 1.41) or methylphenyl silicone oil (n=1.43 to 1.57) can be adjusted by changing the chain length of the methyl group or phenyl group. As such, a mixture of multiple silicone oils with adjusted refractive indexes can also be used as the liquid 90. The refractive index of the liquid 90 is determined by the mixing ratio of the respective silicone oils, so it can easily be made to be similar to the refractive index of the tempered glass 200.

[0024] The refractive index of the liquid 90 does not have to be exactly the same as the refractive index of the strengthened glass 200. The difference in refractive index between the strengthened glass 200 and the liquid 90 is preferably ±0.03 or less, more preferably ±0.02 or less, and even more preferably ±0.01 or less. If the liquid 90 is not provided, scattered light occurs between the strengthened glass 200 and the light supply member 40, making it difficult to obtain data within a range of about 20 μm. However, this can be improved by providing a liquid 90 with such a refractive index difference.

[0025] If the thickness of the liquid 90 is 10 μm or more, scattered light is suppressed to about 10 μm or less, so it is preferable that the thickness of the liquid 90 is 10 μm or more. In principle, the thickness of the liquid 90 can be any thickness, but considering the handling of the liquid, it is preferable that the thickness be 500 μm or less.

[0026] When the refractive index of the light supply member 40 is np and the refractive index of the liquid 90 is nl, if the critical angle θ = arc·sin(nl / np) is larger than the incident angle of the laser light L, total reflection occurs and the laser light L does not enter the liquid 90, so the condition is that the critical angle θ must be sufficiently smaller than the incident angle. For example, if np = 1.52 and the incident angle of the laser light L is 15 degrees, nl must be 1.468 or more.

[0027] The laser light L passing through the tempered glass 200 contains a small amount of scattered light L S Scattered light L S The brightness of the laser beam L varies depending on the polarization phase difference of the scattered portion of the laser beam L. Also, when the polarization direction of the laser beam L is θ s2 The laser light source 10 is installed so that the angle is 45° (within ±5°). Therefore, birefringence occurs due to the photoelastic effect of stress applied in the in-plane direction of the tempered glass 200, and as the laser light L travels through the tempered glass, the polarization phase difference also changes, and along with this change, the scattered light L S The brightness of the light also changes. The polarization retardation is a retardation caused by birefringence.

[0028] The laser beam L is incident on the surface 210 of the tempered glass at an angle of θ s1 is set to 10° or more and 30° or less. This is because if it is less than 10°, the laser light propagates on the glass surface due to the optical waveguiding effect, making it impossible to obtain information about the inside of the glass. Conversely, if it exceeds 30°, the depth resolution inside the glass relative to the laser optical path length decreases, which is not preferable as a measurement method. Therefore, it is preferable to set θ s1 Set to =15°±5°.

[0029] Next, the imaging element 60 will be described with reference to FIG. 2. FIG. 2 is a view of the stress measuring device according to the first embodiment as viewed from the H direction in FIG. 1, and is a diagram showing the positional relationship of the imaging element 60. The polarized light of the laser light L is incident at an angle of 45° with respect to the surface 210 of the strengthened glass 200. This is because the stress in the strengthened glass is parallel to the surface 210. By polarizing the light at an angle of 45° with respect to the surface 210, the phase difference of the laser light L changes due to the stress in the strengthened glass as it travels through the strengthened glass, and the scattering intensity of the scattered light Ls emitted at an angle of 45° with respect to the surface 210 of the strengthened glass 200 changes significantly. Therefore, the scattered light L emitted at an angle of 45° with respect to the surface of this strengthened glass S 2, the image sensor 60 is installed in a direction of 45° with respect to the surface 210 of the tempered glass 200. That is, in FIG. s2 =45°.

[0030] In addition, scattered light L due to the laser light L is scattered between the image pickup element 60 and the laser light L. S A light conversion member 50 is inserted so that the image is formed on the imaging element 60. The light conversion member 50 can be, for example, a glass convex lens or a lens made up of a combination of multiple convex and concave lenses. In this case, a large numerical aperture (NA) of the lens is preferable because it reduces noise caused by laser speckles. Furthermore, by increasing the NA, the light collection rate increases and the sensitivity also increases.

[0031] Furthermore, by using a telecentric lens in which the chief ray is parallel to the optical axis for a lens made up of a combination of multiple lenses, it is possible to form an image using only the light scattered in all directions from the laser light L, mainly scattered in a 45° direction (toward the image sensor) relative to the glass surface of the tempered glass 200. As a result, unnecessary light such as diffuse reflection on the glass surface can be reduced.

[0032] Furthermore, an optical wavelength selection member 80 is inserted between the laser light L and the imaging element 60 to remove light unnecessary for stress measurement. The optical wavelength selection member 80 should have a transmittance of 50% or less, preferably 10% or less, for light having wavelengths other than the wavelength of the laser light L. Furthermore, it is preferable that the width of the wavelengths transmitted through the optical wavelength selection member 80 is about ±10 nm or less with respect to the target wavelength. By inserting the optical wavelength selection member 80, Raman scattered light, fluorescent light, and extraneous light generated by the laser light L and unnecessary for stress measurement are removed, and scattered light L necessary for stress measurement is removed. S Only the light having the wavelength of interest can be collected on the image pickup element 60. As the light wavelength selection member 80, for example, a band-pass filter or a short-pass filter made of multiple dielectric films can be used.

[0033] The imaging element 60 may be, for example, a CCD (Charge Coupled Device) element or a CMOS (Complementary Metal Oxide Semiconductor) sensor element. Although not shown in FIGS. 1 and 2, the CCD element or CMOS sensor element is connected to a control circuit that controls the element and extracts an electrical image signal from the element, a digital image data generation circuit that converts the electrical signal into digital image data, and a digital recording device that records multiple copies of the digital image data. Furthermore, the digital image data generation circuit and the digital recording device are connected to a calculation unit 70.

[0034] The calculation unit 70 has a function of taking in image data from the image sensor 60, or a digital image data generation circuit or digital recording device connected to the image sensor 60, and performing image processing and numerical calculations. The calculation unit 70 may also have other functions (for example, a function of controlling the light intensity and exposure time of the laser light source 10). The calculation unit 70 includes, for example, a CPU (Central Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory), main memory, etc.

[0035] 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 the CPU. The CPU of the calculation unit 70 can read and store data from RAM as necessary. However, part or all of the calculation unit 70 may be realized solely by hardware. The calculation unit 70 may also physically include multiple devices. For example, a personal computer can be used as the calculation unit 70. The calculation unit 70 may also have the functions of a digital image data generation circuit and a digital recording device.

[0036] The polarization phase difference variable member 30 changes the polarization phase difference over time when the light is incident on the tempered glass 200. The polarization phase difference to be changed is, for example, equal to or greater than 1 time the wavelength λ of the laser light. The polarization phase difference must be uniform with respect to the wavefront of the laser light L. For example, a quartz wedge does not produce a uniform polarization phase difference in the direction of the inclined surface of the wedge, and therefore the wavefront of the laser light is not uniform. For this reason, it is not preferable to use a quartz wedge as the polarization phase difference variable member 30.

[0037] An example of a polarization phase difference variable member 30 that can electrically vary the polarization phase difference by 1λ or more uniformly across the wavefront of laser light is a liquid crystal element. The liquid crystal element can vary the polarization phase difference by applying a voltage to the element, and for example, when the wavelength of laser light is 630 nm, the wavelength can be varied by 3 to 6 wavelengths. In the liquid crystal element, the maximum value of the polarization phase difference that can be varied by applying a voltage is determined by the size of the cell gap.

[0038] In a typical liquid crystal element, the cell gap is several μm, so the maximum polarization phase difference is about 1 / 2λ (several hundred nm). Furthermore, displays using liquid crystal do not require any change beyond this. In contrast, when the wavelength of the laser light is, for example, 630 nm, the liquid crystal element used in this embodiment needs to vary the polarization phase difference by about 2000 nm, which is about three times 630 nm, and a cell gap of 20 to 50 μm is required.

[0039] The voltage applied to the liquid crystal element is not proportional to the polarization phase difference. As an example, Figure 3 shows the relationship between the applied voltage and polarization phase difference for a liquid crystal element with a cell gap of 30 μm. In Figure 3, the vertical axis represents the polarization phase difference (number of wavelengths relative to a wavelength of 630 nm), and the horizontal axis represents the voltage applied to the liquid crystal element (plotted logarithmically).

[0040] The polarization phase difference can be varied by approximately 8λ (5000 nm) when the voltage applied to the liquid crystal element is between 0V and 10V. However, in liquid crystal elements, the alignment of the liquid crystal is generally not stable at low voltages between 0V and 1V, and the polarization phase difference fluctuates with temperature changes, etc. Furthermore, when the voltage applied to the liquid crystal element is 5V or higher, the polarization phase difference changes little with changes in voltage. In the case of this liquid crystal element, by using an applied voltage between 1.5V and 5V, the polarization phase difference can be stably varied from 4λ to 1λ, or approximately 3λ.

[0041] When a liquid crystal element is used as the polarization phase difference variable member 30, the polarization phase difference variable member 30 is connected to a liquid crystal control circuit that controls the liquid crystal, and is controlled in synchronization with the image pickup element 60. In this case, it is necessary to vary the polarization phase difference linearly over time and synchronize it with the timing of image pickup by the image pickup element 60.

[0042] Figure 3 is a diagram illustrating the relationship between the voltage applied to a liquid crystal element and the polarization phase difference. As shown in Figure 3, the voltage applied to the liquid crystal element and the polarization phase difference do not change linearly. Therefore, it is necessary to generate a signal that causes the polarization phase difference to change linearly within a certain period of time and apply it as a drive voltage to the liquid crystal element.

[0043] FIG. 4 is a diagram illustrating a circuit for generating a drive voltage that causes the polarization phase difference of a liquid crystal element to change linearly with time.

[0044] 4, digital data storage circuit 301 stores voltage values ​​corresponding to the polarization phase difference for changing the polarization phase difference at regular intervals as digital data in address order within the required range of polarization phase difference change, based on data obtained by measuring in advance the voltage applied to the liquid crystal element used and the polarization phase difference. Table 1 shows an example of some of the digital data stored in digital data storage circuit 301. The voltage column in Table 1 is the digital data to be stored, and represents the voltage value for each 10 nm change in polarization phase difference.

[0045] [Table 1] The clock signal generating circuit 302 generates a clock signal with a constant frequency using a quartz oscillator, etc. The clock signal generated by the clock signal generating circuit 302 is input to the digital data storage circuit 301 and the DA converter 303.

[0046] The DA converter 303 is a circuit that converts the digital data from the digital data storage circuit 301 into an analog signal. Digital data of voltage values ​​stored in the digital data storage circuit 301 are sequentially read out and sent to the DA converter 303 in accordance with the clock signal generated by the clock signal generation circuit 302.

[0047] The DA converter 303 converts the digital data of the voltage value read out at regular time intervals into an analog voltage. The analog voltage output from the DA converter 303 is applied to the liquid crystal element used as the polarization phase difference variable member 30 via a voltage amplifier circuit 304.

[0048] Although not shown in Figure 4, the drive circuit for this liquid crystal element is synchronized with the circuit that controls the image sensor 60 in Figure 2, and when the application of the drive voltage to the liquid crystal element begins, the image sensor 60 begins capturing images continuously over time.

[0049] Fig. 5 is a diagram illustrating an example of a scattered light image at a certain moment of laser light L formed on an imaging element. In Fig. 5, the depth from surface 210 of tempered glass 200 increases as one goes up. In Fig. 5, point A is surface 210 of tempered glass 200, and since the scattered light at surface 210 of tempered glass 200 is strong, the scattered light image spreads out in an elliptical shape.

[0050] Since a strong compressive stress is applied to the surface of the tempered glass 200, birefringence caused by the photoelastic effect causes the polarization phase difference of the laser light L to change with depth. Therefore, the scattered light luminance of the laser light L also changes with depth. The principle by which the scattered light luminance of laser light changes due to internal stress in tempered glass is explained, for example, in Yogyo-Kyokai-Shi (Journal of the Ceramic Industry Association) 80{4} 1972, etc.

[0051] The polarization phase difference variable member 30 can continuously change over time the polarization phase difference of the laser light L before it is incident on the strengthened glass 200. As a result, at each point in the scattered light image of Fig. 5, the scattered light luminance changes according to the polarization phase difference changed by the polarization phase difference variable member 30.

[0052] FIG. 6 is a diagram illustrating the temporal change in the luminance of scattered light (scattered light luminance) at points B and C in FIG. 5. The temporal change in scattered light luminance changes periodically with a period of the wavelength λ of the laser light, according to the polarization phase difference changed by the polarization phase difference variable member 30. For example, in FIG. 6, the period of change in scattered light luminance is the same at points B and C, but the phases are different. This is because when the laser light L travels from point B to point C, the polarization phase difference is further changed due to birefringence caused by stress in the strengthened glass 200. The phase difference δ between points B and C is δ=q / λ, where q is the path difference representing the change in polarization phase difference when the laser light L travels from point B to point C, and λ is the wavelength of the laser light.

[0053] Considering locally, the phase F of the periodic change in scattered light luminance accompanying the change in the temporal polarization phase difference of the polarization phase difference variable member 30 at an arbitrary point S on the laser light L is expressed as a function F(s) at a position s along the laser light L, and the differential value dF / ds with respect to s is the amount of birefringence generated by the in-plane stress of the strengthened glass 200. From the photoelastic constant C of the strengthened glass 200 and dF / ds, the stress σ in the in-plane direction of the strengthened glass 200 at the point S can be calculated using the following equation 1 (mathematical expression 1):

[0054]

number

[0055] On the other hand, the polarization phase difference variable member 30 changes the polarization phase difference continuously over time, for example, by one wavelength or more, within a certain period of time. Within that period of time, the image sensor 60 records a plurality of temporally continuous scattered light images of the laser light L. Then, the temporal change in luminance at each point of these continuously captured scattered light images is measured.

[0056] The scattered light at each point in this scattered light image changes periodically, and the period is constant regardless of location. Therefore, the period T is measured from the change in scattered light luminance at a certain point. Alternatively, the period T can be the average of the periods at multiple points.

[0057] When the polarization phase difference variable member 30 is used to change the polarization phase difference by one wavelength or more (one period or more), the scattered light luminance also changes by one period or more. Therefore, the period T can be measured from the difference between multiple peaks and valleys, or the difference in the time at which the amplitude passes through the midpoint. However, it is difficult to determine one period from data of one period or less.

[0058] In data on the periodic change of scattered light at a certain point, the phase F at that point can be accurately determined using the least squares method of trigonometric functions or Fourier integral based on the period T determined above.

[0059] By using the least squares method or Fourier integration of trigonometric functions with a known period T, only the phase component with the known period T is extracted, making it possible to remove noise with other periods. Furthermore, the longer the temporal change in the data, the higher the removal ability becomes. Normally, the scattered light intensity is weak and the amount of actual phase change is small, so measurement is required using data obtained by varying the polarization phase difference by several λ.

[0060] By measuring data on the temporal change in scattered light at each point in the scattered light image along the laser beam L on the image captured by the image sensor 60 and determining the phase F for each point in the same manner as above, it is possible to determine the phase F of the scattered light brightness along the laser beam L. Figure 7 shows an example of the phase of the scattered light change according to the glass depth.

[0061] For the phase F of the scattered light brightness along this laser light L, the differential value at the coordinate on the laser light L is calculated, and the stress value at the coordinate s on the laser light L can be found using Equation 1. Furthermore, by converting the coordinate s to the distance from the glass surface, the stress value for the depth from the surface of the tempered glass can be calculated. Figure 8 shows an example of the stress distribution found using Equation 1 based on the phase data of the scattered light change in Figure 7.

[0062] Figure 9 shows examples of actual scattered light images at different times t1 and t2, and point A in Figure 9 is the surface of tempered glass. In Figure 9, it can be seen that the scattered light image of laser light has different brightness at each point, and that even at the same point, the brightness distribution at time t2 is not the same as the brightness distribution at time t1. This is because the phase of the periodic scattered light brightness change is shifted.

[0063] In the stress measuring device 1, it is preferable that the laser light L travels on the focal plane of the imaging element 60 which is inclined at 45° with respect to the surface 210 of the strengthened glass 200. This will be described with reference to FIGS.

[0064] 10 is a diagram showing an example of an undesirable design of a plane 250 in tempered glass along which the laser light L propagates. In FIG. 10, the plane 250 in tempered glass 200 along which the laser light L propagates is perpendicular to the surface 210 of the tempered glass 200.

[0065] Fig. 10(b) is a view from direction H of Fig. 10(a). As shown in Fig. 10(b), the imaging element 60 is installed at an angle of 45° with respect to the surface 210 of the tempered glass 200, and the laser light L is observed from an oblique angle of 45°. In the case of Fig. 10, if the distances from two different points, point A and point B, on the laser light L to the imaging element 60 are distance A and distance B, respectively, the distances are different. In other words, it is not possible to focus on point A and point B simultaneously, and it is not possible to obtain a good image of the scattered light of the laser light L in the required area.

[0066] 11 is a diagram showing a preferred design example of a plane 250 in tempered glass through which laser light L propagates. In FIG. 11, plane 250 in tempered glass 200 through which laser light L propagates is inclined at 45° with respect to surface 210 of tempered glass 200.

[0067] 11(b) is a view from direction H of FIG. 11(a). As shown in FIG. 11(b), as in the case of FIG. 10, the imaging element 60 is installed at a 45° angle with respect to the surface 210 of the strengthened glass 200, and the plane 250 along which the laser light L travels is also tilted at a 45° angle to coincide with the focal plane of the imaging element 60. Therefore, the distances to the imaging element 60 (distances A and B) are the same at any point on the laser light L, and a scattered light image of the laser light L in the required area can be captured as a good image. This is possible by rotating the traveling direction of the laser light L by 15°, which is the same angle as the incident angle of the laser light L, with respect to an axis perpendicular to the surface 210 of the strengthened glass 200.

[0068] The NA of the light converting member 50 is increased to reduce speckle noise and improve sensitivity, but an increase in NA reduces the focal depth of the light converting member 50. For this reason, by tilting the traveling plane 250 of the laser light L, which serves as the imaging plane of the laser light L in the tempered glass 200, by 45° with respect to the surface 210 of the tempered glass 200 and aligning it with the focal plane of the imaging element 60, the image of the laser light L on the imaging element 60 can be focused at any point on the laser light L, which is extremely important for acquiring a good image.

[0069] (Position detection 1 on the surface 210 of the tempered glass 200) 12 is a diagram illustrating laser light reflected on the surface of tempered glass. For convenience of explanation, FIG. 12 shows that laser light L is incident on the upper side of tempered glass 200. In FIG. 12, surface S 45 is a virtual plane inclined at 45 degrees with respect to the surface 210 of the tempered glass 200, and the surface S -45 is a virtual plane inclined at -45 degrees with respect to the surface 210 of the tempered glass 200. That is, the plane S 45 and surface S -45 The angle between them is 90 degrees. The absolute values ​​of θ1 shown in FIG. 12 are all 45 degrees.

[0070] In the example of FIG. 12, the laser light L strikes the surface S 45 The laser beam L is incident on the liquid 90 and the tempered glass 200 along the plane S and is inclined at an angle θ2 when viewed from a direction parallel to the surface 210 of the tempered glass 200. When the laser beam L passes through the liquid 90 and is incident on the tempered glass 200, a small amount of reflected light Lr is generated. -45 The laser light L travels through the liquid 90 along the line S. The intersection I between the trajectory of the reflected light Lr traveling through the liquid 90 and the trajectory of the laser light L traveling through the liquid 90 and the tempered glass 200 is the position of the surface 210 of the tempered glass 200. Therefore, if the refractive indexes of the liquid 90 and the tempered glass are approximately the same, the laser light L is hardly refracted, and therefore, the surface S 45 is a plane that is substantially the same as the plane 250 through which the laser light L travels.

[0071] If the refractive indexes of the tempered glass 200 and the liquid 90 are perfectly matched, no reflected light Lr will be generated. Therefore, when using reflected light Lr to identify the surface position, the refractive indexes of the tempered glass 200 and the liquid 90 are shifted within a range such that the difference in refractive index between them is, for example, ±0.02 or less. Furthermore, it is preferable that the liquid 90 contains a fluorescent agent or a filler. This increases the intensity of scattered light in the liquid 90, thereby improving the accuracy of detecting the position of the surface 210 of the tempered glass 200.

[0072] In Fig. 12, the arrow M indicates the direction in which the laser light L and the reflected light Lr are imaged. -45 13 includes a scattered light image generated in the liquid 90 by the reflected light Lr of the laser light L that is reflected by the surface 210 of the strengthened glass 200 when it is incident on the strengthened glass 200, and a scattered light image generated in the strengthened glass 200 by the laser light L.

[0073] The calculation unit 70 can identify the position of the surface 210 of the strengthened glass 200 by using the scattered light image generated in the liquid 90 by the reflected light Lr in the position detection image and the scattered light image generated in the strengthened glass 200 by the laser light L. The calculation unit 70 can detect, for example, an intersection I between an extension line of the scattered light image generated by the reflected light Lr in the position detection image and the scattered light image generated by the laser light L as the position of the surface 210 of the strengthened glass 200.

[0074] As shown in FIG. 12, when θ2 is approximately 15 degrees, the laser light L is incident on the surface S 45 The reflected light Lr is incident on the tempered glass 200 along the -45The reflected light Lr travels approximately along the surface of the tempered glass 200. Therefore, as shown in FIG. 13, the scattered light image of the reflected light Lr is captured so as to extend in a direction parallel to the interface between the liquid 90 and the tempered glass 200 and to substantially overlap with the interface. In this case, the calculation unit 70 may detect the position of the scattered light image generated by the reflected light Lr in the position detection image as the position of the surface 210 of the tempered glass 200. With this method, the calculation unit 70 can detect the position of the surface 210 of the tempered glass 200 without obtaining the intersection point I, thereby simplifying image processing. Note that although the case where θ2 is approximately 15 degrees has been described here, θ2 may be any other angle.

[0075] In addition, in FIG. 12 and FIG. 13, the surface S -45 In the example shown above, an image for position detection is acquired from a direction parallel to the plane S. -45 Even when the position detection image is acquired from a direction non-parallel to the direction of the reflected light Lr traveling through the liquid 90, the position of the surface 210 of the tempered glass 200 can be identified by finding the intersection I between the trajectory of the reflected light Lr traveling through the liquid 90 and the trajectory of the laser light L traveling through the liquid 90 and the tempered glass 200.

[0076] Fig. 14 is a diagram illustrating an example of functional blocks of the calculation unit 70 of the stress measuring device 1. As shown in Fig. 14, the calculation unit 70 has a luminance change measuring means 701, a phase change calculating means 702, a surface position detecting means 703, and a stress distribution calculating means 704. The stress measuring device 1 can measure the stress distribution of the strengthened glass by the luminance change measuring means 701, the phase change calculating means 702, the surface position detecting means 703, and the stress distribution calculating means 704 of the calculation unit 70.

[0077] (Measurement flow of stress distribution in tempered glass) Fig. 15 is a flowchart illustrating a measurement method of the stress measuring apparatus 1. The flow of measuring the stress distribution of strengthened glass by the stress measuring apparatus 1 will be described with reference to Figs.

[0078] First, in step S401, the polarization phase difference of the laser light from the polarized laser light source 10 or the polarized laser light source 10 is varied continuously in time by, for example, one or more wavelengths relative to the wavelength of the laser light using the polarization phase difference varying member 30 (polarization phase difference varying process).

[0079] Next, in step S402, the laser light with the variable polarization phase difference is incident obliquely onto the surface 210 of the strengthened glass 200, which is the object to be measured, via the light supplying member 40 (light supplying step).

[0080] Next, in step S403, the imaging element 60 captures scattered light caused by the laser light with a variable polarization phase difference traveling through the strengthened glass 200 a plurality of times at predetermined time intervals to obtain a plurality of images (imaging step).

[0081] Next, in step S404, the brightness change measuring means 701 of the calculation unit 70 uses multiple images of the scattered light obtained in the imaging process spaced apart in time to measure the periodic brightness change of the scattered light that accompanies the temporal change in the polarization phase difference varied in the polarization phase difference varying process (brightness change measuring process).

[0082] Next, in step S405, the phase change calculation means 702 of the calculation unit 70 calculates the phase change of the periodic luminance change of the scattered light along the laser light incident on the strengthened glass 200 (phase change calculation step).

[0083] Next, in step S406, the calculation unit 70 calculates the stress distribution in the depth direction from the surface 210 of the strengthened glass 200 based on the phase change of the periodic brightness change of the scattered light along the laser light incident on the strengthened glass 200 (stress distribution calculation step). Specifically, first, the surface position detection means 703 of the calculation unit 70 detects the position of the surface 210 of the strengthened glass 200. Next, the stress distribution calculation means 704 of the calculation unit 70 calculates the stress distribution in the depth direction based on the position of the surface 210 detected by the surface position detection means 703. This makes it possible to obtain a depth accuracy of about ±1 μm. The calculated stress distribution may be displayed on a display device (such as a liquid crystal display).

[0084] An example of a specific method for detecting the position of the surface 210 of the strengthened glass 200 will be described with reference to FIG. 16 . FIG. 16 shows an example of a position detection image, in which a scattered light image of the laser light L and a scattered light image of the reflected light Lr are captured. As shown in FIG. 16 , the surface position detection means 703 of the calculation unit 70 first specifies a measurement range M1 for the scattered light image of the laser light L and a measurement range M2 for the scattered light image of the reflected light Lr. Next, the surface position detection means 703 approximates the amount of light in a direction perpendicular to the traveling direction of the reflected light Lr at multiple positions within the measurement range M2 in the traveling direction of the reflected light Lr with a Gaussian distribution and determines the vertex of the Gaussian distribution. Then, the surface position detection means 703 draws a line S1 passing through the vertex of the Gaussian distribution at each position. Next, the surface position detection means 703 determines, for example, an intersection I between the central axis Lc of the scattered light image of the laser light L and the line S1. The intersection I corresponds to the surface 210 of the strengthened glass 200.

[0085] Note that, in the vicinity of θ2=15 degrees, the straight line S1 becomes approximately parallel to the boundary between the liquid 90 and the strengthened glass 200. In this case, as described above, the calculation unit 70 may detect the position of the scattered light image generated by the reflected light Lr in the position detection image as the position of the surface 210 of the strengthened glass 200, without determining the intersection I. In other words, instead of drawing the straight line S1 passing through the apex of the Gaussian distribution at each position, the apex of the Gaussian distribution at one of the positions may be determined, and the position of the determined apex may be set as the position of the surface 210 of the strengthened glass 200.

[0086] In this way, in the stress measurement device 1, the calculation unit 70 automatically detects the position of the surface 210 of the tempered glass 200 based on a position detection image obtained by simultaneously capturing the scattered light generated in the liquid 90 and the scattered light generated in the tempered glass 200 on the same screen. With this method, even if the position of the tempered glass 200 varies when it is set in the stress measurement device 1, the position of the surface 210 of the tempered glass 200 can be identified with high accuracy from the scattered light image before calculating the stress distribution, enabling highly accurate measurement of the stress distribution. In other words, the detection accuracy of the position of the tempered glass surface can be improved compared to the detection of the position of the tempered glass surface based on mechanical positional relationships employed in conventional stress measurement devices. As a result, a depth accuracy of approximately ±1 μm can be achieved in stress measurement, enabling highly accurate stress measurement.

[0087] The multiple images captured by the imaging element 60 preferably include multiple position detection images obtained by simultaneously capturing the scattered light of the reflected light Lr generated in the liquid 90 and the scattered light of the laser light L generated in the strengthened glass 200 on the same screen. The calculation unit 70 preferably detects the position of the surface 210 of the strengthened glass 200 based on the multiple position detection images. The calculation unit 70 detects the position of the surface 210 of the strengthened glass 200 based on, for example, an average value or a peak value of numerical values ​​obtained from the multiple position detection images captured by the imaging element 60. This improves the accuracy of detecting the position of the surface 210 of the strengthened glass 200.

[0088] Furthermore, unlike stress measurement devices that use surface guided light, the stress measurement device 1 does not perform stress measurement that depends on the refractive index distribution of the tempered glass, but performs measurement based on scattered light. Therefore, regardless of the refractive index distribution of the tempered glass (independent of the refractive index distribution of the tempered glass), the stress distribution of the tempered glass can be measured from the outermost surface to deeper parts than before. For example, stress measurement is also possible for lithium aluminosilicate tempered glass, which has the characteristic that the refractive index increases with depth from a certain depth.

[0089] Furthermore, the polarization phase difference of the laser light is varied continuously over time by, for example, one or more wavelengths relative to the wavelength of the laser light using the polarization phase difference varying member 30. This makes it possible to determine the phase of the periodic luminance variation of the scattered light using the least-squares method of trigonometric functions or Fourier integration. Unlike conventional methods that detect the phase from changes in the positions of the wave peaks and valleys, the least-squares method of trigonometric functions and Fourier integration handle all wave data and are based on a known period, making it possible to remove noise of other periods. As a result, it becomes possible to easily and accurately determine the phase of the periodic luminance variation of the scattered light.

[0090] <Modification of the first embodiment> In the modified example of the first embodiment, an example of detecting the position of the surface of strengthened glass by a method different from that of the first embodiment will be described. Note that in the modified example of the first embodiment, the description of the same components as those of the already described embodiment may be omitted.

[0091] (Position detection 2 of the surface 210 of the tempered glass 200) Fig. 17 is a diagram (part 1) showing changes in the phase difference of laser light. For ease of explanation, Fig. 17 shows a diagram in which laser light L is incident from above tempered glass 200. Fig. 17(a) shows a scattered light image of laser light L traveling through liquid 90 and tempered glass 200, and Fig. 17(b) shows changes over time in the brightness of scattered light at points P1 to P5 in Fig. 17(a).

[0092] As described with reference to Fig. 6 etc., a strong compressive stress is applied to the surface portion of the strengthened glass 200, and therefore, due to birefringence caused by the photoelastic effect, the polarization phase difference of the laser light L changes with depth. In detail, at the surface portion of the strengthened glass 200, the temporal change in scattered light luminance changes periodically with a period of the wavelength λ of the laser light L in accordance with the polarization phase difference changed by the polarization phase difference variable member 30. On the other hand, because no stress is applied to the liquid 90, or even if stress is applied, the liquid is isotropic and does not cause birefringence, and the phase of the laser light L traveling through the liquid 90 is constant.

[0093] 17(b), the phase of the laser light L is the same at points P1, P2, and P3, and the phase starts to change when the laser light L travels from point P3 to point P4 and is incident on the tempered glass 200. In the example of FIG. 17(b), the phase difference between the laser light L at points P3 and P4 is δ1, and the phase difference between the laser light L at points P4 and P5 is δ2.

[0094] Fig. 18 is a diagram (part 2) showing changes in the phase difference of laser light. As explained in Fig. 17, as shown in Fig. 18, the phase of laser light L is constant before it is incident on tempered glass 200 and begins to change upon incidence on tempered glass 200. Therefore, the calculation unit 70 can identify the surface 210 of the tempered glass 200 by detecting the point at which the phase of laser light L begins to change. Note that the phase of laser light L can be determined based on the measurement results by measuring data on the temporal change in scattered light at each point of the scattered light image along the laser light L on the image captured by the image sensor 60.

[0095] In this way, the calculation unit 70 calculates the phase of the scattered light generated in the liquid 90 (for convenience, referred to as the first phase) and the phase of the scattered light generated in the strengthened glass 200 (for convenience, referred to as the second phase) from the position detection image, and can detect the position of the surface of the strengthened glass based on the difference between the first phase and the second phase. Here, since the first phase is constant, the calculation unit 70 can detect the inflection point between the first phase and the second phase as the position of the surface 210 of the strengthened glass 200.

[0096] The multiple images captured by the imaging element 60 preferably include multiple position detection images obtained by simultaneously capturing the scattered light generated in the liquid 90 and the scattered light generated in the strengthened glass 200 on the same screen. The calculation unit 70 preferably detects the position of the surface 210 of the strengthened glass 200 based on an average value, a peak value, or the like of the numerical values ​​obtained from the multiple position detection images captured by the imaging element 60. This improves the accuracy of detecting the position of the surface 210 of the strengthened glass 200.

[0097] (Position detection 3 on the surface 210 of the tempered glass 200) Fig. 19 is a diagram showing changes in the brightness of laser light. For ease of explanation, Fig. 19 shows a diagram in which laser light L is incident from above the tempered glass 200. Fig. 19(a) shows a scattered light image of laser light L traveling through the liquid 90 and the tempered glass 200, and Fig. 19(b) shows the brightness of the scattered light at points P1 and P2 in Fig. 19(a).

[0098] 19, the brightness of scattered light typically differs between in liquid 90 and in tempered glass 200. Therefore, surface 210 of tempered glass 200 can be detected based on the change in brightness of scattered light. For example, the midpoint between the brightness at point P1 and the brightness at point P2 can be determined as surface 210. Alternatively, the brightness of scattered light can be measured at more points, and the point where the brightness changes can be determined as surface 210.

[0099] In order to approximate the refractive index of the tempered glass 200, for example, an organic solvent or silicone oil is used as the liquid 90. In general, organic solvents and silicone oils have large molecules, so the scattered light is stronger in the liquid 90 than in the tempered glass 200. However, depending on the type of tempered glass, the scattered light may be weaker in the liquid 90 than in the tempered glass. Even in such cases, the surface 210 can be detected by utilizing the difference in the intensity of the scattered light between the liquid 90 and the tempered glass.

[0100] In this way, the calculation unit 70 calculates the brightness of the scattered light image generated in the liquid 90 (for convenience, referred to as the first brightness) and the brightness of the scattered light image generated in the strengthened glass 200 (for convenience, referred to as the second brightness) from the position detection image, and can detect the position of the surface 210 of the strengthened glass 200 based on the difference between the first brightness and the second brightness.

[0101] The multiple images captured by the imaging element 60 preferably include multiple position detection images obtained by simultaneously capturing the scattered light generated in the liquid 90 and the scattered light generated in the strengthened glass 200 on the same screen. The calculation unit 70 preferably detects the position of the surface 210 of the strengthened glass 200 based on an average value, a peak value, or the like of the numerical values ​​obtained from the multiple position detection images captured by the imaging element 60. This improves the accuracy of detecting the position of the surface 210 of the strengthened glass 200.

[0102] For example, the calculation unit 70 may calculate a first average value of the brightness of the scattered light generated in the liquid 90 and a second average value of the brightness of the scattered light generated in the tempered glass 200 from multiple position detection images, and detect the position of the surface 210 of the tempered glass 200 based on the difference between the first average value and the second average value.

[0103] (Position detection 4 on the surface 210 of the tempered glass 200) Fig. 20 is a diagram showing changes in the trajectory of the laser light. For ease of explanation, Fig. 20 shows that the laser light L is incident on the strengthened glass 200 from above.

[0104] 20 , when the refractive index of liquid 90 and the refractive index of strengthened glass 200 differ, the laser light is refracted at the interface between liquid 90 and strengthened glass 200, and the trajectory of the scattered light of laser light L is curved rather than straight. Therefore, calculation unit 70 can detect, as the position of surface 210 of strengthened glass 200, an intersection I between the trajectory of the scattered light image generated in liquid 90 by laser light L and the trajectory of the scattered light image generated in strengthened glass 200 by laser light L.

[0105] The multiple images captured by the imaging element 60 preferably include multiple position detection images obtained by simultaneously capturing the scattered light generated in the liquid 90 and the scattered light generated in the strengthened glass 200 on the same screen. The calculation unit 70 preferably detects the position of the surface 210 of the strengthened glass 200 based on an average value, a peak value, or the like of the numerical values ​​obtained from the multiple position detection images captured by the imaging element 60. This improves the accuracy of detecting the position of the surface 210 of the strengthened glass 200.

[0106] 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.

[0107] For example, the position detections 1 to 4 of the surface 210 of the tempered glass 200 can be combined as appropriate. For example, the calculation unit 70 may have all of the functions of the position detections 1 to 4 of the surface 210 of the tempered glass 200. In this case, the calculation unit 70 can perform the position detection of the surface 210 of the tempered glass 200 by selecting any one of the position detections 1 to 4 of the surface 210 of the tempered glass 200. Furthermore, the calculation unit 70 may perform the position detection of the surface 210 of the tempered glass 200 by combining any two or more of the position detections 1 to 4 of the surface 210 of the tempered glass 200.

[0108] In addition to the above-described embodiments, the following supplementary notes are also disclosed. (Appendix 1) a polarization phase difference variable member that varies the polarization phase difference of the laser light; a light supplying member that causes the laser light, the polarization phase difference of which has been varied, to enter a tempered glass object to be measured; a liquid disposed between the light supply member and the tempered glass; a light converting member that forms an image of scattered light of the laser light that passes through the light supplying member and the liquid and is incident on the strengthened glass; an imaging element that captures an image of the scattered light formed on the light converting member a plurality of times at predetermined time intervals to obtain a plurality of images; a calculation unit that measures a periodic luminance change of the scattered light using the plurality of images, calculates a phase change of the luminance change, and calculates a stress distribution in a depth direction from a surface of the strengthened glass based on the phase change, the plurality of images include a plurality of position detection images obtained by simultaneously capturing the scattered light generated in the liquid and the scattered light generated in the strengthened glass on the same screen, The calculation unit detects the position of the surface of the tempered glass based on the plurality of position detection images. (Appendix 2) 2. The stress measuring device for strengthened glass described in Appendix 1, wherein each of the position detection images includes a first scattered light image generated in the liquid by reflected light of the laser light that is reflected on a surface of the strengthened glass when it is incident on the strengthened glass, and a second scattered light image generated in the strengthened glass by the laser light. (Appendix 3) 3. The stress measuring device for strengthened glass described in Appendix 2, wherein the calculation unit detects the intersection of an extension line of the first scattered light image in the position detection image and the second scattered light image as the position of the surface of the strengthened glass. (Appendix 4) the first scattered light image in the position detection image extends in a direction parallel to an interface between the liquid and the strengthened glass, 3. The strengthened glass stress measuring device according to claim 2, wherein the calculation unit detects the position of the first scattered light image in the position detection image as the position of the surface of the strengthened glass. (Appendix 5) 5. The stress measuring device for strengthened glass according to claim 1, wherein the calculation unit calculates a first phase of the scattered light generated in the liquid and a second phase of the scattered light generated in the strengthened glass from the plurality of position detection images, and detects the position of the surface of the strengthened glass based on a difference between the first phase and the second phase. (Appendix 6) 6. The device for measuring stress in strengthened glass according to claim 5, wherein the calculation unit detects an inflection point between the first phase and the second phase as a position on a surface of the strengthened glass. (Appendix 7) 7. The stress measuring device for strengthened glass according to claim 1, wherein the calculation unit calculates a first luminance of the scattered light generated in the liquid and a second luminance of the scattered light generated in the strengthened glass from the plurality of position detection images, and detects the position of the surface of the strengthened glass based on a difference between the first luminance and the second luminance. (Appendix 8) The stress measuring device for strengthened glass described in Appendix 7, wherein the calculation unit calculates a first average value of the brightness of the scattered light generated in the liquid and a second average value of the brightness of the scattered light generated in the strengthened glass from the multiple position detection images, and detects the position of the surface of the strengthened glass based on the difference between the first average value and the second average value. (Appendix 9) 9. The stress measuring device for strengthened glass according to claim 1, wherein the calculation unit detects an intersection between a trajectory of a scattered light image generated in the liquid by the laser light and a trajectory of a scattered light image generated in the strengthened glass by the laser light as a position of a surface of the strengthened glass. (Appendix 10) 10. The apparatus for measuring stress in strengthened glass according to any one of claims 1 to 9, wherein a difference in refractive index between the strengthened glass and the liquid is ±0.02 or less. (Appendix 11) 11. The stress measuring device for tempered glass according to claim 1, wherein the liquid contains a fluorescent agent or a filler. (Appendix 12) a polarization phase difference varying step of varying the polarization phase difference of the laser light; an imaging step of forming an image of scattered light emitted by the laser light, the polarization phase difference of which has been varied, passing through a light supply member and a liquid and incident on a tempered glass, using a light conversion member, and capturing an image of the scattered light formed on the light conversion member multiple times at predetermined time intervals using an image sensor to obtain multiple images; a stress distribution calculation step of measuring a periodic luminance change of the scattered light using the plurality of images, calculating a phase change of the luminance change, and calculating a stress distribution in a depth direction from the surface of the strengthened glass based on the phase change, the plurality of images include a plurality of position detection images obtained by simultaneously capturing the scattered light generated in the liquid and the scattered light generated in the strengthened glass on the same screen, A method for measuring stress in tempered glass, wherein the stress distribution calculation step detects the position of the surface of the tempered glass based on a plurality of the position detection images, and then calculates the stress distribution in the depth direction from the surface of the tempered glass. [Explanation of symbols]

[0109] 1. Stress measurement device 10 Laser light source 20 Polarizing element 30 Polarization phase difference variable member 40 Light supply member 40x recesses 50 Light conversion material 60 image sensor 70 Arithmetic section 80 Optical wavelength selection member 90 liquid 200 tempered glass 210 Tempered Glass Surface 250 The surface on which the laser light L travels 301 Digital Data Storage Circuit 302 Clock signal generating circuit 303 DA converter 304 Voltage Amplifier Circuit 701 Luminance change measuring means 702 Phase change calculation means 703 Surface position detection means 704 Stress distribution calculation method

Claims

1. a polarization phase difference variable member that varies the polarization phase difference of the laser light; a light supplying member that causes the laser light, the polarization phase difference of which has been varied, to enter a tempered glass object to be measured; a liquid disposed between the light supply member and the tempered glass; a light converting member that forms an image of scattered light of the laser light that passes through the light supplying member and the liquid and is incident on the strengthened glass; an imaging element that captures an image of the scattered light formed on the light converting member a plurality of times at predetermined time intervals to obtain a plurality of images; a calculation unit that measures a periodic luminance change of the scattered light using the plurality of images, calculates a phase change of the luminance change, and calculates a stress distribution in a depth direction from a surface of the strengthened glass based on the phase change, the plurality of images include a plurality of position detection images obtained by simultaneously capturing the scattered light generated in the liquid and the scattered light generated in the strengthened glass on the same screen, The calculation unit detects the position of the surface of the tempered glass based on the plurality of position detection images.

2. 2. The device for measuring stress in strengthened glass according to claim 1, wherein each of the position detection images includes a first scattered light image generated in the liquid by reflected light of the laser light that is reflected on a surface of the strengthened glass when it is incident on the strengthened glass, and a second scattered light image generated in the strengthened glass by the laser light.

3. 3. The apparatus for measuring stress in strengthened glass according to claim 2, wherein the calculation unit detects an intersection of an extension of the first scattered light image in the position detection image and the second scattered light image as the position of the surface of the strengthened glass.

4. the first scattered light image in the position detection image extends in a direction parallel to an interface between the liquid and the strengthened glass, The apparatus for measuring stress in strengthened glass according to claim 2 , wherein the calculation unit detects the position of the first scattered light image in the position detection image as the position of the surface of the strengthened glass.

5. 2. The stress measuring device for strengthened glass according to claim 1, wherein the calculation unit calculates a first phase of the scattered light generated in the liquid and a second phase of the scattered light generated in the strengthened glass from the plurality of position detection images, and detects a position of the surface of the strengthened glass based on a difference between the first phase and the second phase.

6. The apparatus for measuring stress in strengthened glass according to claim 5 , wherein the calculation unit detects an inflection point between the first phase and the second phase as a position on the surface of the strengthened glass.

7. 2. The strengthened glass stress measuring device according to claim 1, wherein the calculation unit calculates a first luminance of the scattered light generated in the liquid and a second luminance of the scattered light generated in the strengthened glass from the plurality of position detection images, and detects a position of the surface of the strengthened glass based on a difference between the first luminance and the second luminance.

8. 8. The stress measuring device for strengthened glass according to claim 7, wherein the calculation unit calculates a first average value of the luminance of the scattered light generated in the liquid and a second average value of the luminance of the scattered light generated in the strengthened glass from the plurality of position detection images, and detects the position of the surface of the strengthened glass based on a difference between the first average value and the second average value.

9. 2. The stress measuring device for strengthened glass according to claim 1, wherein the calculation unit detects an intersection between a trajectory of a scattered light image generated in the liquid by the laser light and a trajectory of a scattered light image generated in the strengthened glass by the laser light as a position of a surface of the strengthened glass.

10. The apparatus for measuring stress in strengthened glass according to claim 1 , wherein a difference in refractive index between the strengthened glass and the liquid is ±0.02 or less.

11. The device for measuring stress in strengthened glass according to claim 1 , wherein the liquid contains a fluorescent agent or a filler.

12. a polarization phase difference varying step of varying the polarization phase difference of the laser light; an imaging step of forming an image of scattered light emitted by the laser light, the polarization phase difference of which has been varied, passing through a light supply member and a liquid and incident on a tempered glass, using a light conversion member, and capturing an image of the scattered light formed on the light conversion member multiple times at predetermined time intervals using an image sensor to obtain multiple images; a stress distribution calculation step of measuring a periodic luminance change of the scattered light using the plurality of images, calculating a phase change of the luminance change, and calculating a stress distribution in a depth direction from the surface of the strengthened glass based on the phase change, the plurality of images include a plurality of position detection images obtained by simultaneously capturing the scattered light generated in the liquid and the scattered light generated in the strengthened glass on the same screen, A method for measuring stress in tempered glass, wherein the stress distribution calculation step detects the position of the surface of the tempered glass based on a plurality of the position detection images, and then calculates the stress distribution in the depth direction from the surface of the tempered glass.

Images