Tempered glass stress measurement device and tempered glass stress measurement method

Abstract

The invention provides a stress measuring device for tempered glass and a stress measuring method for tempered glass, which can improve the detection accuracy of the position of the surface of tempered glass in the stress measuring device for tempered glass. This tempered glass stress measurement device is provided with: a polarized light phase difference variable member that varies the polarized light phase difference of laser light; a light supply means for causing the laser beam having the variable polarization phase difference to enter tempered glass, which is an object to be measured; a liquid disposed between the light supply member and the tempered glass; a light conversion member that forms an image of scattered light of the laser light incident on the tempered glass via the light supply member and the liquid; an imaging element that acquires a plurality of images by imaging the scattered light imaged by the light conversion member a plurality of times at predetermined time intervals; and a calculation unit that measures a periodic brightness change in the scattered light using the plurality of images, calculates a phase change in the brightness change, and calculates a stress distribution in the depth direction from the surface of the tempered glass on the basis of 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 tempered glass on the same screen. The calculation unit detects the position of the surface of the tempered glass on the basis of the plurality of position detection images.

Description

Technical Field

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

[0002] Various stress measurement devices are known for measuring stress in an object in a non-destructive manner. For example, a stress measurement device includes: a variable polarization phase difference component that varies the polarization phase difference of laser light relative to the wavelength of the laser light; an imaging element that captures scattered light emitted by the variable polarization phase difference laser light incident on tempered glass a plurality of times at predetermined time intervals to obtain a plurality of images; and a computing unit that uses the plurality of images to measure periodic brightness variations of the scattered light, calculates phase variations of the brightness variations, and calculates stress distribution in the depth direction from the surface of the tempered glass based on the phase variations (see, for example, Patent Document 1).

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: International Publication No. 2018 / 056121 Summary of the Invention

[0006] Problems to be solved by the invention

[0007] The stress distribution in chemically strengthened glass occurs at a depth of approximately ten to several hundred μm from the surface. In particular, the stress variation within tens of μm near the surface is significant relative to the depth. Therefore, measuring the stress distribution requires high spatial resolution in the depth direction, requiring a depth accuracy of approximately ±1 μm. Furthermore, to achieve this depth accuracy, the position of the strengthened glass surface must be detected with an accuracy comparable to or greater than this depth accuracy.

[0008] However, conventional stress measurement devices detect the position of the tempered glass surface based on mechanical positional relationships. Consequently, the position of the tempered glass surface may deviate from the correct position by several to tens of μm due to factors such as temperature fluctuations in the environment in which the stress measurement device is used and friction with the stress measurement device.

[0009] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to improve the detection accuracy of the position of the surface of a tempered glass in a tempered glass stress measuring device.

[0010] Technical solutions to problems

[0011] A stress measuring device for tempered glass comprises: a variable polarization phase difference member for varying the polarization phase difference of laser light; a light supply member for causing the laser light with a variable polarization phase difference to be incident on a tempered glass object to be measured; a liquid disposed between the light supply member and the tempered glass; a light conversion member for forming an image of scattered light of the laser light incident on the tempered glass via the light supply member and the liquid; an imaging element for capturing the scattered light formed by the light conversion member a plurality of times at predetermined time intervals to obtain a plurality of images; and a calculation unit for measuring periodic brightness variations of the scattered light using the plurality of images, calculating phase variations of the brightness variations, and calculating a stress distribution in a depth direction from the surface of the tempered glass based on the phase variations. 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 tempered 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.

[0012] Effects of the Invention

[0013] According to the disclosed technology, in a stress measuring device for tempered glass, it is possible to improve the detection accuracy of the position of the surface of the tempered glass. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a diagram illustrating a stress measurement device according to the first embodiment.

[0015] Figure 2 It is from Figure 1 FIG. 1 is a diagram showing the stress measurement device according to the first embodiment as viewed in the H direction.

[0016] Figure 3 This is a diagram illustrating the relationship between the applied voltage of a liquid crystal element and the polarization phase difference.

[0017] Figure 4 This is a diagram illustrating a circuit for generating a driving voltage that causes a liquid crystal element to change its polarization phase difference linearly with time.

[0018] Figure 5 This is a diagram illustrating a scattered light image of the laser light L formed on the imaging element at a certain moment.

[0019] Figure 6 This is an example Figure 5 Graph showing the temporal variation of the brightness of scattered light at points B and C.

[0020] Figure 7 This is a diagram illustrating how the phase of scattered light changes according to the depth of glass.

[0021] Figure 8 This example is based on Figure 7 Phase data of scattered light changes and stress distribution obtained using Equation 1.

[0022] Figure 9 3 is a diagram illustrating actual scattered light images at different times t1 and t2.

[0023] Figure 10 This is a diagram showing an undesirable design example of the traveling surface 250 of the laser light L in the tempered glass.

[0024] Figure 11 1 is a diagram showing a preferred design example of a traveling surface 250 of the laser beam L in the tempered glass.

[0025] Figure 12 This is a diagram illustrating laser light reflected on the surface of tempered glass.

[0026] Figure 13 This is a schematic diagram of an image for position detection.

[0027] Figure 14 1 is a diagram illustrating functional blocks of the computing unit 70 of the stress measuring device 1 .

[0028] Figure 15 This is a flowchart illustrating an evaluation method using the stress measurement device 1 .

[0029] Figure 16 This is an example of an image for position detection.

[0030] Figure 17 This is a diagram showing changes in the phase difference of laser light (Part 1).

[0031] Figure 18 This is a diagram showing changes in the phase difference of laser light (part 2).

[0032] Figure 19 It is a graph showing changes in the brightness of laser light.

[0033] Figure 20 This is a diagram showing changes in the trajectory of the laser beam. DETAILED DESCRIPTION

[0034] Hereinafter, the embodiment of the present invention will be described with reference to the accompanying drawings. In the drawings, the same components are sometimes denoted by the same reference numerals, and repeated descriptions are omitted.

[0035] <First embodiment>

[0036] (Stress measuring device)

[0037] Figure 1 FIG is a diagram illustrating a stress measuring device according to the first embodiment. Figure 1 As shown, the stress measurement 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 conversion member 50 , an imaging element 60 , a calculation unit 70 , an optical wavelength selection member 80 , and a liquid 90 .

[0038] The stress measurement device 1 modulates the polarization phase difference of laser light relative to its wavelength, for example, by one wavelength or more. The device then captures scattered light emitted by the laser light incident on the tempered glass, with the variable polarization phase difference, multiple times at predetermined time intervals to obtain multiple images. The device then uses these multiple images to measure the periodic brightness variations of the scattered light, calculates the phase variation associated with the brightness variations, and calculates the stress distribution based on the phase variation. This is described in detail below.

[0039] exist Figure 1 In FIG. 2 , 200 denotes a tempered glass to be measured. The tempered glass 200 is glass that has been tempered by, for example, chemical tempering, air-cooling tempering, or the like.

[0040] The laser light source 10 is arranged so as to inject laser light L from the light supply member 40 into the surface layer of the tempered glass 200 , and the polarization phase difference variable member 30 is inserted between the laser light source 10 and the light supply member 40 .

[0041] As the laser light source 10, for example, a semiconductor laser, a helium-neon laser, or an argon laser can be used. Semiconductor lasers generally have polarized light, and semiconductor lasers with wavelengths such as 405nm, 520nm, 630nm, and 850nm are put to practical use. The shorter the wavelength of the laser, the smaller the beam diameter, and the more the spatial resolution can be improved. In addition, there is a tendency that the shorter the wavelength of the laser, the smaller the laser speckle noise, and therefore it is preferred. In addition, the laser needs to transmit the measurement object.

[0042] In order to improve the resolution in the depth direction of the tempered glass 200, it is preferred that the position of the minimum beam diameter of the laser be located within the ion exchange layer of the tempered glass 200, and the minimum beam diameter be 20 μm or less. It is further preferred that the position of the minimum beam diameter of the laser be located on the surface 210 of the tempered glass 200. It should be noted that since the beam diameter of the laser becomes the resolution in the depth direction, it is necessary to set the beam diameter to be less than the required depth resolution. Here, the beam diameter refers to 1 / e when the brightness at the center of the beam is maximum. 2 (about 13.5%) of the width, in the case of an elliptical or sheet-like beam shape, the beam diameter means the minimum width. However, in this case, it is necessary to make the minimum width of the beam diameter toward the depth direction of the glass.

[0043] Since the cross-sectional shape of the light beam emitted from a semiconductor laser is typically elliptical, shaping it into a circular shape using a beam shaping element can improve spatial resolution and thus enhance measurement accuracy. Furthermore, while the output distribution within the beam shape of the light beam emitted from a semiconductor laser is typically Gaussian, shaping it into a more consistent distribution within the beam shape, such as a top-hat distribution, using an output distribution shaping element can also enhance measurement accuracy.

[0044] The beam shaping member and the output distribution shaping member are, for example, inserted between the laser light source 10 and the polarization phase difference variable member 30. Examples of the beam shaping member include cylindrical lenses, anamorphic prisms, and apertures. Examples of the output distribution shaping member include aspherical lenses and DOEs (diffractive optical elements).

[0045] The polarizing member 20 is inserted between the laser light source 10 and the variable polarization phase difference member 30 as needed. Specifically, when the laser light L emitted by the laser light source 10 is not polarized, the polarizing member 20 is inserted between the laser light source 10 and the variable polarization phase difference member 30. When the laser light L emitted by 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 arranged so that the polarization plane of the laser light L is at a 45° angle relative to the surface 210 of the tempered glass 200. For example, a polarizing plate fixed to a predetermined polarization direction can be used as the polarizing member 20, but other members having the same function may also be used.

[0046] The light supply member 40 is placed in optical contact with the surface 210 of the tempered glass 200, serving as the object to be measured, via the liquid 90. The light supply member 40 has the function of allowing light from the laser light source 10 to enter the tempered glass 200. For example, a prism made of optical glass can be used as the light supply member 40. In this case, in order for light to optically enter the surface 210 of the tempered glass 200 through the prism, the refractive index of the prism must be approximately the same as that of the tempered glass 200 (within ±0.2).

[0047] The liquid 90 is disposed between the light supply member 40 and the tempered glass 200. Figure 1 In the example shown in FIG. 4 , a recess 40x is provided on the surface of the light supply member 40, and the recess 40x is filled with a liquid 90. The recess 40x can be formed, for example, by grinding or etching the surface of the light supply member 40. It should be noted that the bottom of the recess 40x does not need to be flat. For example, the recess 40x can be formed into a spherical shape similar to a concave lens.

[0048] The refractive index of the tempered glass 200 slightly varies depending on the type of tempered glass. Therefore, in order to achieve an "appropriate" refractive index for the light supply member 40, the light supply member 40 must be replaced according to the type of tempered glass. However, this replacement process is inefficient. Therefore, 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 on the tempered glass 200. The "appropriate refractive index" will be discussed later.

[0049] As liquid 90, for example, a mixture of 1-bromonaphthalene (n=1.64) and xylene (n=1.50) can be used. As liquid 90, a mixture of multiple silicone oils with different structures can also be used. For example, dimethyl silicone oil (n=1.38-1.41) and methylphenyl silicone oil (n=1.43-1.57) can adjust the refractive index by changing the chain length of each methyl group and phenyl group. A mixture of multiple silicone oils with adjusted refractive index can also be used as liquid 90. The refractive index of liquid 90 is determined by the mixing ratio of each, so it can easily be made to be similar to the refractive index of tempered glass 200.

[0050] It should be noted that the refractive index of the liquid 90 does not have to be exactly the same as that of the tempered glass 200. The refractive index difference between the tempered 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. Without the liquid 90, scattered light occurs between the tempered glass 200 and the light supply member 40, making it difficult to obtain data within a range of approximately 20 μm. However, the placement of the liquid 90 with such a refractive index difference can improve this situation.

[0051] If the thickness of liquid 90 is 10 μm or greater, scattered light is suppressed to approximately 10 μm or less, so it is preferably 10 μm or greater. In principle, the thickness of liquid 90 may be any thickness, but considering liquid handling, it is preferably 500 μm or less.

[0052] It should be noted that, assuming 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 greater than the incident angle of the laser light L, total internal reflection occurs, and the laser light L does not enter the liquid 90. Therefore, it is necessary that the critical angle θ is 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 needs to be at least 1.468.

[0053] The laser light L passing through the tempered glass 200 generates a small amount of scattered light L S . Scattered light L SThe brightness of the laser light L varies according to the polarization phase difference of the scattered portion of the laser light L. In addition, the polarization direction of the laser light L is adjusted relative to the surface 210 of the tempered glass 200. Figure 2 θ s2 The laser light source 10 is set so as to be 45° (within ±5°). Therefore, due to the photoelastic effect of the stress applied to the in-plane direction of the tempered glass 200, birefringence is caused. As the laser light L travels in the tempered glass, the polarization phase difference also changes. With this change, the scattered light L S The brightness of the light also changes. It should be noted that the so-called polarization phase difference is the phase difference (retardation) caused by birefringence.

[0054] In addition, the laser light L is directed toward the surface 210 of the tempered glass. s1 The angle is set to be between 10° and 30°. This is because if it is less than 10°, the laser propagates on the glass surface due to the optical waveguide effect, and information inside the glass cannot be obtained. On the other hand, if it exceeds 30°, the depth resolution inside the glass relative to the laser optical path length decreases, which is not a good measurement method. Therefore, it is preferably set to θ s1 =15°±5°.

[0055] Next, use Figure 2 The imaging element 60 will be described. Figure 2 It is from Figure 1 The figure showing the positional relationship of the imaging element 60 when observing the stress measuring device according to the first embodiment from the H direction is shown. The polarized light of the laser light L is incident at an angle of 45° relative to the surface 210 of the tempered glass 200. This is because the stress in the tempered glass is horizontal at the surface 210. By making the polarized light 45° relative to the surface 210, as the laser light L travels in the tempered glass, the phase difference changes according to the stress in the tempered glass, and the scattered light Ls emitted at an angle of 45° relative to the surface 210 of the tempered glass 200 has a significantly changed scattering intensity. Therefore, it is necessary to capture the scattered light Ls emitted at an angle of 45° relative to the surface of the tempered glass. S ,exist Figure 2 In FIG. 2 , the imaging element 60 is set at a 45° angle relative to the surface 210 of the tempered glass 200. Figure 2 In, θ s2 =45°.

[0056] In addition, a light conversion member 50 is inserted between the imaging element 60 and the laser light L so that the scattered light L based on the laser light L SThe image is formed on the imaging element 60. As the light conversion member 50, for example, a glass convex lens or a combination of multiple convex and concave lenses can be used. In this case, a larger numerical aperture (NA) is preferred because it reduces noise caused by laser speckle. Furthermore, increasing the NA increases the light focusing efficiency and improves sensitivity.

[0057] Furthermore, by forming a telecentric lens with a principal ray parallel to the optical axis, a lens composed of multiple lenses can be used to form an image using only the light scattered in all directions by the laser light L, primarily scattered in the 45° direction (toward the imaging element) relative to the glass surface of the tempered glass 200. As a result, unwanted light, such as diffuse reflections from the glass surface, can be reduced.

[0058] In addition, 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 sets the transmittance of light having wavelengths other than the wavelength of the laser light L to 50% or less, preferably to 10% or less. In addition, the wavelength width of the transmitted light wavelength selection member 80 is preferably about ±10nm or less relative to the target wavelength. By inserting the optical wavelength selection member 80, Raman scattered light, fluorescence, and extraneous light generated by the laser light L that are unnecessary for stress measurement can be removed, and only the scattered light L required for stress measurement can be transmitted. S The light is collected in the imaging element 60. As the optical wavelength selection member 80, for example, a bandpass filter or a shortpass filter formed by multi-layered dielectric films can be used.

[0059] As the imaging element 60, for example, a CCD (Charge Coupled Device) element or a CMOS (Complementary Metal Oxide Semiconductor) sensor element can be used. Figure 1 and Figure 2 Although not shown, the CCD element and the CMOS sensor element are connected to a control circuit that controls the element and extracts an electrical signal of an image 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 a plurality of digital image data. Furthermore, the digital image data generation circuit and the digital recording device are connected to the calculation unit 70.

[0060] The computing unit 70 has the function of receiving 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 computing unit 70 may also have other functions (for example, a function for controlling the light intensity and exposure time of the laser light source 10). The computing unit 70 includes, for example, a CPU (Central Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory), main memory, and the like.

[0061] In this case, the various functions of the operation unit 70 can be realized by reading programs stored in ROM, etc., into main memory and executing them by the CPU. The CPU of the operation unit 70 can read or store data from RAM as needed. However, part or all of the operation unit 70 can also be realized solely by hardware. In addition, the operation unit 70 can also physically include multiple devices. For example, a personal computer can be used as the operation unit 70. In addition, the operation unit 70 can also function as a digital image data generation circuit or a digital recording device.

[0062] The variable polarization phase difference member 30 varies the polarization phase difference of incident light on the tempered glass 200 over time. The varying polarization phase difference is, for example, at least one 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 crystal wedge exhibits non-uniform polarization phase difference along the wedge's inclined surface, resulting in a non-uniform wavefront for the laser light. Therefore, using a crystal wedge as the variable polarization phase difference member 30 is not preferred.

[0063] An example of a variable polarization phase difference member 30 that is uniform on the wavefront of the laser light and can electrically vary the polarization phase difference by more than 1λ is a liquid crystal element. A liquid crystal element can vary the polarization phase difference by applying a voltage to the element. For example, if the wavelength of the laser light is 630nm, it can vary by three to six wavelengths. In a liquid crystal element, the maximum value of the variable polarization phase difference that can be achieved by applying a voltage is determined by the size of the cell gap.

[0064] The cell gap of a typical liquid crystal element is several μm, so the maximum polarization phase difference is about 1 / 2λ (several hundred nm). Furthermore, displays using liquid crystals do not require changes beyond this. In contrast, the liquid crystal element used in this embodiment requires a variable polarization phase difference of approximately 2000 nm, which is about three times the wavelength of 630 nm, when the laser wavelength is, for example, 630 nm. This requires a cell gap of 20 to 50 μm.

[0065] The voltage applied to the liquid crystal element is not proportional to the polarization phase difference. As an example, the relationship between the applied voltage and the polarization phase difference of a liquid crystal element with a cell gap of 30 μm is shown in FIG. Figure 3 .exist Figure 3 In FIG. 1 , the vertical axis represents the polarization phase difference (in terms of wavelength relative to a wavelength of 630 nm), and the horizontal axis represents the voltage applied to the liquid crystal element (plotted logarithmically).

[0066] The voltage applied to the liquid crystal element is 0V to 10V, which can adjust the polarization phase difference of approximately 8λ (5000nm). However, the liquid crystal orientation of the liquid crystal is generally unstable at low voltages of 0V to 1V, and the polarization phase difference fluctuates due to temperature changes, etc. In addition, when the voltage applied to the liquid crystal element is 5V or above, the polarization phase difference changes less with respect to the voltage change. In the case of this liquid crystal element, by using it at an applied voltage of 1.5V to 5V, the polarization phase difference of 4λ to 1λ, that is, approximately 3λ, can be stably adjusted.

[0067] When a liquid crystal element is used as the variable polarization phase difference element 30, the variable polarization phase difference element 30 is connected to a liquid crystal control circuit that controls the liquid crystal and is controlled in synchronization with the imaging element 60. In this case, the polarization phase difference needs to be linearly variable over time and synchronized with the timing of imaging by the imaging element 60.

[0068] Figure 3 : is a diagram illustrating the relationship between the applied voltage of the liquid crystal element and the polarization phase difference. Figure 3 As shown in FIG, the applied voltage and polarization phase difference of the liquid crystal element 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 to the liquid crystal element as a driving voltage.

[0069] Figure 4 This is a diagram illustrating a circuit for generating a driving voltage that causes a liquid crystal element to change its polarization phase difference linearly with time.

[0070] exist Figure 4 In the digital data storage circuit 301, based on data obtained by previously measuring the applied voltage and polarization retardation of the liquid crystal element used, voltage values ​​corresponding to the polarization retardation, which are used to change the polarization retardation at a constant interval, are recorded as digital data in address order within the desired polarization retardation change range. Table 1 illustrates a portion of the digital data recorded in the digital data storage circuit 301. The voltage column in Table 1 represents the recorded digital data and is the voltage value for each 10 nm change in the polarization retardation.

[0071]

Table 1

[0072] The clock signal generating circuit 302 generates a clock signal having a constant frequency using a crystal 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 .

[0073] The DA converter 303 converts digital data from the digital data storage circuit 301 into an analog signal. Based on the clock signal generated by the clock signal generation circuit 302, the digital data of the voltage values ​​sequentially stored in the digital data storage circuit 301 is read and sent to the DA converter 303.

[0074] The digital data of the voltage value read out at constant time intervals is converted into an analog voltage by the DA converter 303. The analog voltage output from the DA converter 303 is applied to the liquid crystal element serving as the polarization phase difference variable member 30 via the voltage amplifier circuit 304.

[0075] It should be noted that although Figure 4 Not shown in the figure, but the driving circuit and control circuit of the liquid crystal element Figure 2 The circuits of the imaging element 60 are synchronized, and at the same time as the driving voltage starts to be applied to the liquid crystal element, the imaging element 60 starts to capture images continuously in time.

[0076] Figure 5 This is a diagram illustrating a scattered light image of the laser light L formed on the imaging element at a certain moment. Figure 5 In the figure, the depth from the surface 210 of the tempered glass 200 increases as the depth increases upward. Figure 5 In FIG. 2 , point A is the surface 210 of the strengthened glass 200 . The scattered light on the surface 210 of the strengthened glass 200 is strong, so the scattered light image expands in an elliptical shape.

[0077] Because strong compressive stress is applied to the surface of tempered glass 200, the polarization phase difference of laser light L varies with depth due to birefringence caused by the photoelastic effect. Consequently, the brightness of the scattered light of laser light L also varies with depth. It should be noted that the principle by which the brightness of scattered laser light varies depending on the internal stress of tempered glass is described, for example, in Yogyo-Kyokai-Shi (Ceramic Industry Association Journal) 80{4}1972.

[0078] The polarization phase difference variable member 30 can continuously change the polarization phase difference of the laser light L before entering the tempered glass 200. Figure 5 At each point of the scattered light image, the scattered light brightness changes according to the polarization phase difference changed by the polarization phase difference variable member 30.

[0079] Figure 6 This is an example Figure 5The temporal variation of the brightness of the scattered light at points B and C (scattered light brightness) is shown in FIG. The temporal variation of the scattered light brightness varies periodically with the 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, Figure 6 In the figure, the period of change in scattered light brightness at points B and C is the same, but the phases are different. This is because as laser light L travels from point B to point C, the polarization phase difference further changes due to birefringence caused by stress in tempered glass 200. Regarding the phase difference δ between points B and C, if q is the value of the polarization phase difference that changes when laser light L travels from point B to point C, expressed as the optical path length difference, and λ is the wavelength of the laser light, then δ = q / λ.

[0080] Considering this locally, the function F(s) represents the phase F of the periodic change in the brightness of scattered light associated with the temporal change in the polarization phase difference of the polarization phase difference variable member 30 at an arbitrary point S on the laser light L, using the position s along the laser light L. The differential value dF / ds with respect to s represents the amount of birefringence caused by the in-plane stress of the strengthened glass 200. Based on the photoelastic constant C of the strengthened glass 200 and dF / ds, the in-plane stress σ of the strengthened glass 200 at point S can be calculated using the following equation (Mathematical Formula 1).

[0081]

Mathematical formula 1

[0082] Note that, in the stress measurement device 1 , since the laser light L is incident obliquely on the glass, obtaining the stress distribution with respect to the depth in the vertical direction from the glass surface requires conversion from the point s to the depth direction.

[0083] Meanwhile, the polarization phase difference variable element 30 continuously changes the polarization phase difference over a certain period of time, for example, by one wavelength or more. During this period of time, the imaging element 60 records a plurality of temporally continuous scattered light images of the laser light L. The temporal changes in brightness at each point in the scattered light images obtained by these continuous captures are then measured.

[0084] The changes in scattered light at each point in the scattered light image are periodic, and the period is constant regardless of location. Therefore, the period T is measured based on the change in the brightness of the scattered light at a certain point. Alternatively, the average of the periods at multiple points can be used as the period T.

[0085] When the polarization phase difference variable member 30 changes the polarization phase difference by more than one wavelength (one period), the scattered light brightness also changes by more than one period. Therefore, the period T can be measured based on the difference between multiple peaks and troughs, or the difference in the time when the amplitude passes through the midpoint. However, it is difficult to determine the period using data with less than one period.

[0086] In the data of periodic changes in scattered light at a certain point, the phase F at that point can be accurately determined by the least squares method of trigonometric functions and Fourier integration based on the period T determined above.

[0087] 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 can be extracted, removing noise from other periods. Furthermore, the longer the temporal variation of the data, the greater the removal capability. Generally, scattered light has low brightness, and the actual phase variation is also small, necessitating measurement based on variable data with a polarization phase difference of several λ.

[0088] By measuring the temporal variation data of scattered light at each point of the scattered light image along the laser light L on the image captured by the imaging element 60 and calculating the phase F for each data using the same method as described above, the phase F of the scattered light brightness along the laser light L can be calculated. Figure 7 This is an example of how the phase of scattered light changes with the depth of the glass.

[0089] By calculating the differential value at the coordinate s on the laser light L in the phase F of the scattered light brightness along the laser light L, the stress value at the coordinate s on the laser light L can be obtained using Equation 1. Furthermore, by converting the coordinate s into a distance from the glass surface, the stress value relative to the depth from the surface of the tempered glass can be calculated. Figure 8 is based on Figure 7 This is an example of calculating the stress distribution using Equation 1 using phase data of scattered light changes.

[0090] Figure 9 These are examples of actual scattered light images at different times t1 and t2. Figure 9 Point A is the surface of the tempered glass. Figure 9 In the figure, it can be seen that the scattered light image of the laser has different brightness at each point. In addition, even at the same point, the brightness distribution at time t2 is different from the brightness distribution at time t1. This is because the phase of the periodic scattered light brightness change is shifted.

[0091] 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 degrees with respect to the surface 210 of the tempered glass 200. Figure 10 and Figure 11 Explain this.

[0092] Figure 10 : is a diagram showing an undesirable design example of the traveling surface 250 of the laser beam L in the tempered glass. Figure 10 In FIG. 2 , the traveling plane 250 of the laser light L in the strengthened glass 200 is perpendicular to the surface 210 of the strengthened glass 200 .

[0093] Figure 10 (b) is from Figure 10 (a) The image observed from the direction H. Figure 10 As shown in (b), the imaging element 60 is set at an angle of 45° with respect to the surface 210 of the tempered glass 200, and the laser light L is observed at an angle of 45°. Figure 10 In this case, if the distances from two different points on the laser light L, namely point A and point B, to the imaging element 60 are defined as distance A and distance B, the distances are different. In other words, it is impossible to focus on both point A and point B simultaneously, and it is impossible to obtain a good image of the scattered light image of the laser light L in the desired area.

[0094] Figure 11 : is a diagram showing a preferred design example of the traveling surface 250 of the laser light L in the tempered glass. Figure 11 In FIG. 2 , the traveling plane 250 of the laser light L in the strengthened glass 200 is inclined at 45° with respect to the surface 210 of the strengthened glass 200 .

[0095] Figure 11 (b) is from Figure 11 (a) The image observed from the direction H. Figure 11 As shown in (b), Figure 10 Similarly, the imaging element 60 is tilted 45° relative to the surface 210 of the tempered glass 200. However, the propagation plane 250 of the laser light L is also tilted 45° to coincide with the focal plane of the imaging element 60. Therefore, regardless of the point on the laser light L, the distances (distance A and distance B) to the imaging element 60 are the same, allowing a good image of the scattered light image of the laser light L in the desired area to be captured. This is achieved by rotating the propagation direction of the laser light L by an angle of 15°, the same as the incident angle of the laser light L, relative to an axis perpendicular to the surface 210 of the tempered glass 200.

[0096] The NA of the light conversion member 50 is increased to reduce speckle noise and improve sensitivity. However, as the NA increases, the depth of focus of the light conversion member 50 decreases. Therefore, 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, at 45° relative 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 is in focus regardless of any point on the laser light L, which is extremely important for obtaining a good image.

[0097] (Position Detection 1 of Surface 210 of Strengthened Glass 200)

[0098] Figure 12 This figure explains the laser light reflected on the surface of tempered glass. Figure 12 In FIG. 2 , for the sake of convenience, the laser light L is incident from the upper side of the tempered glass 200. Figure 12 Middle, face S 45 is an imaginary plane inclined at 45 degrees with respect to the surface 210 of the tempered glass 200. -45 It is a virtual plane inclined at -45 degrees with respect to the surface 210 of the tempered glass 200. 45 With face S -45 The angle formed is 90 degrees. Figure 12 The absolute value of θ1 shown is 45 degrees in all cases.

[0099] exist Figure 12 In the example, the laser L is along the surface S 45 The laser beam L is incident on the liquid 90 and the tempered glass 200 at an angle of 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 enters the tempered glass 200, some reflected light Lr is generated. However, the reflected light Lr is incident on the surface S. -45 The intersection I of the trajectory of the reflected light Lr traveling in the liquid 90 and the trajectory of the laser light L traveling in the liquid 90 and the tempered glass 200 is located at the surface 210 of the tempered glass 200. Therefore, if the refractive index of the liquid 90 and the tempered glass is substantially the same, the laser light L is hardly refracted, and thus the surface S 45 This is substantially the same surface as the traveling surface 250 of the laser light L described above.

[0100] It should be noted that when the refractive indices of the tempered glass 200 and the liquid 90 are completely identical, no reflected light Lr is generated. Therefore, when using reflected light Lr to determine the surface position, the refractive indices of the tempered glass 200 and the liquid 90 are offset, for example, within a range where the difference between the two refractive indices is ±0.02 or less. Furthermore, the liquid 90 preferably contains a fluorescent agent or filler. This can increase the intensity of scattered light in the liquid 90, thereby improving the accuracy of position detection of the surface 210 of the tempered glass 200.

[0101] exist Figure 12 In FIG. 1 , the arrow M indicates the direction in which the laser light L and the reflected light Lr are photographed. -45 In order to determine the position of the surface 210 of the tempered glass 200, when the laser light L and the reflected light Lr are photographed from the direction of the arrow M by the imaging element 60, the following is obtained: Figure 13 The schematic diagram shows an image for position detection. Figure 13 The position detection image shown includes a scattered light image generated in the liquid 90 by the reflected light Lr of the laser light L reflected from the surface 210 of the strengthened glass 200 when incident on the strengthened glass 200 , and a scattered light image generated in the strengthened glass 200 by the laser light L.

[0102] The calculation unit 70 can determine 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. For example, the calculation unit 70 can detect the intersection I of the extended 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.

[0103] like Figure 12 As shown, when θ2 is approximately 15 degrees, the laser light L is approximately along the surface S. 45 The reflected light Lr is incident on the tempered glass 200 and is approximately along the S -45 Therefore, if Figure 13 As shown, the scattered light image of the reflected light Lr is captured so as to extend parallel to the interface between the liquid 90 and the tempered glass 200, substantially overlapping it. In this case, the computing unit 70 can also 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. This method allows the computing unit 70 to detect the position of the surface 210 of the tempered glass 200 without determining the intersection point I, thereby simplifying image processing. It should be noted that while the angle θ2 is approximately 15 degrees, it can also be an angle other than this.

[0104] It should be noted that in Figure 12 and Figure 13 In the figure, the S -45 An example of obtaining a position detection image in a direction parallel to the plane S -45 When a position detection image is obtained in a non-parallel direction, the position of the surface 210 of the tempered glass 200 can be determined by finding the intersection I between the trajectory of the reflected light Lr traveling in the liquid 90 and the trajectory of the laser light L traveling in the liquid 90 and the tempered glass 200.

[0105] Figure 14 1 is a diagram illustrating the functional blocks of the computing unit 70 of the stress measuring device 1. Figure 14As shown, the computing unit 70 includes a brightness change measuring unit 701, a phase change calculating unit 702, a surface position detecting unit 703, and a stress distribution calculating unit 704. The stress measuring device 1 can measure the stress distribution of the tempered glass using the brightness change measuring unit 701, the phase change calculating unit 702, the surface position detecting unit 703, and the stress distribution calculating unit 704 of the computing unit 70.

[0106] (Measurement process of stress distribution of tempered glass)

[0107] Figure 15 : is a flowchart illustrating a measurement method of the stress measurement device 1. Figure 14 and Figure 15 , the flow of measuring the stress distribution of the tempered glass in the stress measuring apparatus 1 will be described.

[0108] First, in step S401, the polarization phase difference variable component 30 is used to make the polarization phase difference of the laser from the laser light source 10 having polarized light or the laser light source 10 to which polarized light is applied continuously variable in time relative to the wavelength of the laser, for example, by more than one wavelength (polarization phase difference variable process).

[0109] Next, in step S402 , the laser beam with a variable polarization phase difference is made incident on the tempered glass 200 as the object to be measured via the light supply member 40 at an angle with respect to the surface 210 (light supplying step).

[0110] Next, in step S403 , the imaging element 60 captures scattered light generated by the laser beam with variable polarization phase difference traveling through the tempered glass 200 a plurality of times at predetermined time intervals to obtain a plurality of images (imaging step).

[0111] Next, in step S404, the brightness change measuring unit 701 of the operation section 70 uses a plurality of temporally spaced images of the scattered light obtained in the shooting process to measure the periodic brightness changes of the scattered light accompanying the temporal changes in the polarization phase difference that are variable through the polarization phase difference variable process (brightness change measuring process).

[0112] Next, in step S405 , the phase change calculation unit 702 of the calculation unit 70 calculates the phase change along the periodic brightness change of the scattered light of the laser light incident on the tempered glass 200 (phase change calculation step).

[0113] Next, in step S406, the calculation unit 70 calculates the stress distribution in the depth direction from the surface 210 of the tempered glass 200 based on the phase change along the periodic brightness change of the scattered light of the laser light incident on the tempered glass 200 (stress distribution calculation step). Specifically, the surface position detection unit 703 of the calculation unit 70 first detects the position of the surface 210 of the tempered glass 200. Next, the stress distribution calculation unit 704 of the calculation unit 70 calculates the stress distribution in the depth direction using the position of the surface 210 detected by the surface position detection unit 703 as a reference. This achieves a depth accuracy of approximately ±1 μm. It should be noted that the calculated stress distribution can also be displayed on a display device (such as a liquid crystal display).

[0114] Reference Figure 16 An example of a specific method of detecting the position of the surface 210 of the tempered glass 200 will be described. Figure 16 This is an example of an image for position detection, in which scattered light images of laser light L and scattered light images of reflected light Lr are captured. Figure 16 As shown, the surface position detection unit 703 of the computing unit 70 first specifies a measurement range M1 for the scattered light image of laser light L and a measurement range M2 for the scattered light image of reflected light Lr. Next, the surface position detection unit 703 approximates the light intensity in a direction perpendicular to the direction of travel of reflected light Lr with a Gaussian distribution at multiple locations in the measurement range M2, and determines the apex of the Gaussian distribution. A straight line S1 is then drawn passing through the apex of the Gaussian distribution at each location. Next, the surface position detection unit 703 determines, for example, the intersection point I between the central axis Lc of the scattered light image of laser light L and the straight line S1. The intersection point I represents the surface 210 of the tempered glass 200.

[0115] It should be noted that at approximately θ2 = 15 degrees, the straight line S1 is substantially parallel to the boundary between the liquid 90 and the tempered 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 tempered glass 200, rather than determining the intersection I. In other words, rather than drawing a straight line S1 passing through the vertices of the Gaussian distribution at each position, the vertex of the Gaussian distribution at any position may be determined, and the position of the determined vertex may be used as the position of the surface 210 of the tempered glass 200.

[0116] In this manner, in the stress measurement device 1, the computing 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 scattered light generated in the liquid 90 and scattered light generated in the tempered glass 200 on the same screen. This method allows for highly accurate determination of the position of the surface 210 of the tempered glass 200 based on the scattered light image before calculating the stress distribution, even if the position of the tempered glass 200 is misaligned when the tempered glass 200 is placed in the stress measurement device 1. This enables highly accurate stress distribution measurement. This improves the accuracy of the tempered glass surface position detection compared to conventional stress measurement devices that rely on mechanical positional relationships. As a result, a depth accuracy of approximately ±1 μm can be achieved during stress measurement, enabling highly accurate stress measurement.

[0117] It should be noted that the multiple images captured by the imaging element 60 preferably include multiple position detection images obtained by simultaneously capturing scattered light of the reflected light Lr generated in the liquid 90 and scattered light of the laser light L generated in the tempered glass 200 on the same screen. Furthermore, the computing unit 70 preferably detects the position of the surface 210 of the tempered glass 200 based on the multiple position detection images. The computing unit 70 detects the position of the surface 210 of the tempered glass 200 based on, for example, the average value or peak value of the numerical values ​​obtained from the multiple position detection images captured by the imaging element 60. This improves the accuracy of position detection of the surface 210 of the tempered glass 200.

[0118] Furthermore, unlike stress measurement devices that utilize surface optical waveguides, stress measurement in the stress measurement device 1 does not rely on the refractive index distribution of the tempered glass, but rather performs measurement based on scattered light. Therefore, regardless of the refractive index distribution of the tempered glass (regardless of the tempered glass's refractive index distribution), the stress distribution of the tempered glass can be measured from the outermost surface to a deeper depth than conventionally possible. For example, stress measurement can be performed on tempered glass such as lithium aluminosilicate, which has a characteristic of increasing refractive index with depth from a certain depth.

[0119] Furthermore, the polarization phase difference variable element 30 causes the polarization phase difference of the laser light to vary continuously over time relative to the laser wavelength, for example, by one or more wavelengths. Therefore, the phase of the periodic brightness variations of the scattered light can be determined using the least squares method of trigonometric functions and Fourier integration. Unlike conventional methods that detect phase based on changes in the positions of wave crests and troughs, these methods process the entire wave data. Furthermore, based on a pre-known period, noise from other periods can be removed. As a result, the phase of the periodic brightness variations of the scattered light can be easily and accurately determined.

[0120] <Modification of First Embodiment>

[0121] The modification of the first embodiment shows an example in which the position of the surface of the tempered glass is detected by a method different from that of the first embodiment. Note that, in the modification of the first embodiment, descriptions of components identical to those of the already described embodiment may be omitted.

[0122] (Position Detection 2 of Surface 210 of Tempered Glass 200)

[0123] Figure 17 This is a diagram showing the change in the phase difference of the laser (part 1). Figure 17 In FIG. 2 , for convenience of explanation, the laser light L is incident on the tempered glass 200 from above. Figure 17 (a) shows the scattered light image of the laser light L traveling in the liquid 90 and the tempered glass 200. Figure 17 (b) shows Figure 17 Temporal changes in the brightness of scattered light at points P1 to P5 in (a).

[0124] As reference Figure 6 As described in [ 1 ] and [ 2 ], since strong compressive stress is applied to the surface of the tempered glass 200, the polarization phase difference of the laser light L varies with depth due to birefringence caused by the photoelastic effect. Specifically, the temporal variation in the brightness of the scattered light at the surface of the tempered glass 200 changes periodically with the wavelength λ of the laser light L, depending on the polarization phase difference varied by the polarization phase difference variable member 30. Meanwhile, since no stress is applied to the liquid 90, or even if stress is applied, the liquid is isotropic and does not produce birefringence, and the phase of the laser light L propagating through the liquid 90 remains constant.

[0125] Therefore, if Figure 17 As shown in (b), the phase of the laser light L is the same at points P1, P2, and P3, and when the laser light L travels from point P3 to point P4, the phase starts to change from the moment it enters the tempered glass 200. Figure 17 In the example of (b), the phase difference between the laser light L at the point P3 and the point P4 is δ1, and the phase difference between the laser light L at the point P4 and the point P5 is δ2.

[0126] Figure 18 This is a diagram showing the change in the phase difference of the laser (part 2). Figure 17 This is also explained in Figure 18As shown, the phase of the laser light L is constant before entering the tempered glass 200, but begins to change upon entering the 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 the laser light L begins to change. It should be noted that the phase of the laser light L can be determined based on the measurement results by measuring data on temporal changes in scattered light at each point along the scattered light image of the laser light L in the image captured by the imaging element 60.

[0127] In this way, the calculation unit 70 can calculate the phase of the light scattered in the liquid 90 (for convenience, referred to as the first phase) and the phase of the light scattered in the tempered glass 200 (for convenience, referred to as the second phase) based on the position detection image, and detect the position of the surface of the tempered glass based on the difference between the first phase and the second phase. Here, because 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 tempered glass 200.

[0128] It should be noted that the multiple images captured by the imaging element 60 preferably include multiple position detection images obtained by simultaneously capturing scattered light generated in the liquid 90 and scattered light generated in the tempered glass 200 on the same screen. Furthermore, the calculation unit 70 preferably detects the position of the surface 210 of the tempered glass 200 based on the average value, peak value, etc. of the numerical values ​​obtained from the multiple position detection images captured by the imaging element 60. This improves the accuracy of position detection of the surface 210 of the tempered glass 200.

[0129] (Position Detection 3 of the Surface 210 of the Tempered Glass 200)

[0130] Figure 19 This is a graph showing changes in laser brightness. Figure 19 In FIG. 2 , for convenience of explanation, the laser light L is incident on the tempered glass 200 from above. Figure 19 (a) shows the scattered light image of the laser light L traveling in the liquid 90 and the tempered glass 200. Figure 19 (b) shows Figure 19 Brightness of scattered light at points P1 and P2 in (a).

[0131] like Figure 19 As shown, the brightness of scattered light typically differs between liquid 90 and tempered glass 200. Therefore, surface 210 of tempered glass 200 can be detected based on changes in the brightness of scattered light. For example, the midpoint between the brightness at point P1 and the brightness at point P2 can be used as surface 210. Alternatively, the brightness of scattered light can be measured at more points, and the points where the brightness changes can be used as surface 210.

[0132] It should be noted that, in order to approximate the refractive index of tempered glass 200, an organic solvent or silicone oil, for example, is used as liquid 90. Generally speaking, organic solvents and silicone oils have larger molecules, so scattered light in liquid 90 is stronger than in tempered glass 200. However, depending on the type of tempered glass, the scattered light in liquid 90 may be weaker than in tempered glass. In such cases, the difference in the intensity of scattered light in liquid 90 and tempered glass can be used to detect surface 210.

[0133] In this way, the calculation unit 70 can calculate the brightness of the scattered light image generated in the liquid 90 (for convenience, it is set as the first brightness) and the brightness of the scattered light image generated in the tempered glass 200 (for convenience, it is set as the second brightness) based on the position detection image, and detect the position of the surface 210 of the tempered glass 200 based on the difference between the first brightness and the second brightness.

[0134] It should be noted that the multiple images captured by the imaging element 60 preferably include multiple position detection images obtained by simultaneously capturing scattered light generated in the liquid 90 and scattered light generated in the tempered glass 200 on the same screen. Furthermore, the calculation unit 70 preferably detects the position of the surface 210 of the tempered glass 200 based on the average value, peak value, etc. of the numerical values ​​obtained from the multiple position detection images captured by the imaging element 60. This improves the accuracy of position detection of the surface 210 of the tempered glass 200.

[0135] For example, the calculation unit 70 may calculate a first average value of the brightness of scattered light generated in the liquid 90 and a second average value of the brightness of scattered light generated in the tempered glass 200 based on a plurality of 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.

[0136] (Position Detection 4 of the Surface 210 of the Tempered Glass 200)

[0137] Figure 20 This is a diagram showing the change in the trajectory of the laser. Figure 20 In FIG. 2 , for convenience of explanation, the laser light L is incident on the tempered glass 200 from above.

[0138] like Figure 20 As shown, when the refractive index of the liquid 90 differs from that of the tempered glass 200, the laser light is refracted at the interface between the liquid 90 and the tempered glass 200. Therefore, the trajectory of the scattered light of the laser light L is not a straight line but a curved trajectory. Therefore, the calculation unit 70 can detect the intersection I of the trajectory of the scattered light image generated by the laser light L in the liquid 90 and the trajectory of the scattered light image generated by the laser light L in the tempered glass 200 as the position of the surface 210 of the tempered glass 200.

[0139] It should be noted that the multiple images captured by the imaging element 60 preferably include multiple position detection images obtained by simultaneously capturing scattered light generated in the liquid 90 and scattered light generated in the tempered glass 200 on the same screen. Furthermore, the calculation unit 70 preferably detects the position of the surface 210 of the tempered glass 200 based on the average value, peak value, etc. of the numerical values ​​obtained from the multiple position detection images captured by the imaging element 60. This improves the accuracy of position detection of the surface 210 of the tempered glass 200.

[0140] As mentioned above, although the preferred embodiment is described in detail, the present invention is not limited to the above embodiment, and various modifications and substitutions can be made to the above embodiment without departing from the scope described in the claims.

[0141] For example, the position detection functions 1 to 4 for the surface 210 of the tempered glass 200 can be appropriately combined. For example, the computing unit 70 may include all functions for detecting the position of the surface 210 of the tempered glass 200 1 to 4. In this case, the computing unit 70 can detect the position of the surface 210 of the tempered glass 200 by selecting any one of the position detection functions 1 to 4 for the surface 210 of the tempered glass 200. Furthermore, the computing unit 70 may detect the position of the surface 210 of the tempered glass 200 by combining any two or more of the position detection functions 1 to 4 for the surface 210 of the tempered glass 200.

[0142] In addition to the above embodiments, the following supplementary notes are disclosed.

[0143] (Note 1)

[0144] A stress measuring device for tempered glass, comprising:

[0145] A polarization phase difference variable component that makes the polarization phase difference of the laser light variable;

[0146] a light supplying member for causing the laser light with a variable polarization phase difference to be incident on a tempered glass serving as a measured object;

[0147] a liquid disposed between the light-supplying member and the tempered glass;

[0148] a light conversion member for forming an image of scattered light of the laser light incident on the tempered glass via the light supply member and the liquid;

[0149] an imaging element that captures the scattered light formed by the light conversion member a plurality of times at predetermined time intervals to obtain a plurality of images; and

[0150] a calculation unit that measures the periodic brightness change of the scattered light using the plurality of images, calculates a phase change of the brightness change, and calculates a stress distribution in a depth direction from the surface of the tempered glass based on the phase change;

[0151] 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 tempered glass on the same screen.

[0152] The calculation unit detects the position of the surface of the tempered glass based on the plurality of position detection images.

[0153] (Note 2)

[0154] The stress measuring device for tempered glass according to Supplementary Note 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 reflected from a surface of the tempered glass when incident on the tempered glass; and a second scattered light image generated in the tempered glass by the laser light.

[0155] (Note 3)

[0156] In the stress measuring device for tempered glass according to Supplementary Note 2, the computing unit detects an intersection of an extension line of the first scattered light image and the second scattered light image in the position detection image as the position of the surface of the tempered glass.

[0157] (Note 4)

[0158] The stress measuring device for tempered glass according to Appendix 2, wherein:

[0159] The first scattered light image in the position detection image extends in a direction parallel to the interface between the liquid and the tempered glass.

[0160] 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 tempered glass.

[0161] (Note 5)

[0162] The stress measuring device for tempered glass according to any one of Appendixes 1 to 4, wherein the computing unit calculates a first phase of the scattered light generated in the liquid and a second phase of the scattered light generated in the tempered glass based on the plurality of position detection images, and detects the position of the surface of the tempered glass based on a difference between the first phase and the second phase.

[0163] (Note 6)

[0164] In the stress measuring device for tempered glass according to Supplementary note 5, the calculation unit detects an inflection point between the first phase and the second phase as a position on the surface of the tempered glass.

[0165] (Note 7)

[0166] The stress measuring device for tempered glass according to any one of Appendixes 1 to 6, wherein the computing unit calculates a first brightness of the scattered light generated in the liquid and a second brightness of the scattered light generated in the tempered glass based on the plurality of position detection images, and detects the position of the surface of the tempered glass based on the difference between the first brightness and the second brightness.

[0167] (Note 8)

[0168] The stress measuring device for tempered glass according to Supplementary Note 7, wherein the computing 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 tempered glass based on the plurality of position detection images, and detects the position of the surface of the tempered glass based on the difference between the first average value and the second average value.

[0169] (Note 9)

[0170] The stress measuring device for tempered glass according to any one of Appendixes 1 to 8, wherein the computing unit detects an intersection of 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 tempered glass by the laser light as the position of the surface of the tempered glass.

[0171] (Note 10)

[0172] The stress measuring apparatus for tempered glass according to any one of Appendixes 1 to 9, wherein a difference in refractive index between the tempered glass and the liquid is ±0.02 or less.

[0173] (Note 11)

[0174] The stress measuring device for tempered glass according to any one of Appendix 1 to 10, wherein the liquid contains a fluorescent agent or a filler.

[0175] (Note 12)

[0176] A method for measuring stress of tempered glass, comprising:

[0177] Polarization phase difference variable process, making the polarization phase difference of laser light variable;

[0178] a photographing step of forming an image of scattered light emitted by the laser light having a variable polarization phase difference and incident on the tempered glass via the light supply member and the liquid by a light conversion member, and photographing the scattered light formed by the light conversion member a plurality of times at predetermined time intervals using an imaging element to obtain a plurality of images; and

[0179] a stress distribution calculating step of measuring the periodic brightness change of the scattered light using the plurality of images, calculating a phase change of the brightness change, and calculating a stress distribution in a depth direction from the surface of the tempered glass based on the phase change;

[0180] 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 tempered glass on the same screen.

[0181] In the stress distribution calculation step, the position of the surface of the tempered glass is detected based on the plurality of position detection images, and then the stress distribution in the depth direction from the surface of the tempered glass is calculated.

[0182] Label Description

[0183] 1. Stress measuring device;

[0184] 10. Laser light source;

[0185] 20 polarized light components;

[0186] 30. Polarization light phase difference variable component;

[0187] 40 light supply member;

[0188] 40x Depression;

[0189] 50 light conversion component;

[0190] 60 shooting elements;

[0191] 70 Operation unit;

[0192] 80 optical wavelength selection component;

[0193] 90 liquid;

[0194] 200 tempered glass;

[0195] 210 Surface of tempered glass;

[0196] 250 The traveling surface of the laser L;

[0197] 301 digital data storage circuit;

[0198] 302 clock signal generating circuit;

[0199] 303 DA converter;

[0200] 304 voltage amplifier circuit;

[0201] 701 brightness change measurement unit;

[0202] 702 phase change calculation unit;

[0203] 703 surface position detection unit;

[0204] 704 Stress distribution calculation unit.

Claims

1. A stress measuring device for tempered glass, comprising: A polarization phase difference variable component that makes the polarization phase difference of the laser light variable; a light supplying member for causing the laser light with a variable polarization phase difference to be incident on a tempered glass serving as a measured object; a liquid disposed between the light-supplying member and the tempered glass; a light conversion member for forming an image of scattered light of the laser light incident on the tempered glass via the light supply member and the liquid; an imaging element that captures the scattered light formed by the light conversion member a plurality of times at predetermined time intervals to obtain a plurality of images; and a calculation unit that measures the periodic brightness change of the scattered light using the plurality of images, calculates a phase change of the brightness change, and calculates a stress distribution in a depth direction from the surface of the tempered 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 tempered 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. The stress measuring device for tempered 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 beam reflected from a surface of the strengthened glass when incident on the strengthened glass, and a second scattered light image generated in the strengthened glass by the laser beam.

3. The stress measuring device for tempered glass according to claim 2, wherein: The calculation unit detects an intersection point between an extension line of the first scattered light image and the second scattered light image in the position detection image as a position of the surface of the tempered glass.

4. The stress measuring device for tempered glass according to claim 2, wherein: The first scattered light image in the position detection image extends in a direction parallel to the interface between the liquid and the tempered glass. 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 tempered glass.

5. The stress measuring device for tempered 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 tempered glass based on the plurality of position detection images, and detects the position of the surface of the tempered glass based on a difference between the first phase and the second phase.

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

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

8. The stress measuring device for tempered glass according to claim 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 tempered glass based on the plurality of position detection images, and detects the position of the surface of the tempered glass based on a difference between the first average value and the second average value.

9. The stress measuring device for tempered glass according to claim 1, wherein: The calculation unit detects an intersection point 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 tempered glass by the laser light as a position of a surface of the tempered glass.

10. The stress measuring device for tempered glass according to any one of claims 1 to 9, wherein The refractive index difference between the tempered glass and the liquid is ±0.02 or less.

11. The stress measuring device for tempered glass according to any one of claims 1 to 9, wherein The liquid contains a fluorescent agent or a filler.

12. A method for measuring stress in tempered glass, comprising: Polarization phase difference variable process, making the polarization phase difference of laser light variable; a photographing step of forming an image of scattered light emitted by the laser light having a variable polarization phase difference and incident on the tempered glass via the light supply member and the liquid by a light conversion member, and photographing the scattered light formed by the light conversion member a plurality of times at predetermined time intervals using an imaging element to obtain a plurality of images; and a stress distribution calculating step of measuring the periodic brightness change of the scattered light using the plurality of images, calculating a phase change of the brightness change, and calculating a stress distribution in a depth direction from the surface of the tempered 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 tempered glass on the same screen. In the stress distribution calculation step, the position of the surface of the tempered glass is detected based on the plurality of position detection images, and then the stress distribution in the depth direction from the surface of the tempered glass is calculated.

Images