JP2020076598A - Stress measurement device, and stress measurement method - Google Patents

Abstract

To provide a stress measurement device of chemical strengthening glass that has a predictable stress distribution of an entire depth in a short time, and is high in productivity.SOLUTION: The present invention relates to a stress measurement device of chemical strengthening glass 200 including a lithium ion. The stress measurement device has: a light supply member 20; a light take-out member 30; a light conversion member 40; an image pick-up element 60; position measurement means that measures a position from an image; stress distribution calculation means; stress distribution estimation means that estimates a stress distribution of a second region of the chemical strengthening glass on the basis of a stress distribution of a first region to an ion concentration transition point in a depth direction from a surface, and a pre-measured stress distribution of the representative second region of the ion concentration transition point in a deeper depth direction of the chemical strengthening glass; and synthesis means that synthesizes the stress distribution of the first region and the stress distribution of the second region, and calculates an entire stress distribution of the first region and second region.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a stress measuring device and a stress measuring method.

  In electronic devices such as mobile phones and smartphones, glass is often used for the display unit and the case body. For such glass, so-called chemically strengthened glass is used in which the strength is increased by forming a surface layer (ion exchange layer) on the glass surface by ion exchange in order to increase the glass strength.

  The surface layer includes at least a compressive stress layer existing on the glass surface side and in which a compressive stress due to ion exchange is generated, and a tensile stress existing in the glass adjacent to the compressive stress layer and in which a tensile stress is generated. It may include layers.

  As a technique for measuring the stress of the surface layer of the chemically strengthened glass, for example, when the refractive index of the surface layer of the chemically strengthened glass is higher than the internal refractive index, using the optical waveguide effect and the photoelastic effect, A technique for nondestructively measuring the compressive stress of a layer (hereinafter referred to as a nondestructive measurement technique) can be mentioned. In this non-destructive measurement technology, monochromatic light is incident on the surface layer of chemically strengthened glass to generate multiple modes by the optical waveguide effect, light with a fixed ray trajectory is taken out in each mode, and a convex lens corresponds to each mode. Form an image on the bright line. There are as many bright lines as the number of modes formed.

  Further, in this nondestructive measurement technique, the light extracted from the surface layer is configured so that the emission lines can be observed with respect to the emission surface for two types of light components whose light oscillation directions are horizontal and vertical. Using the property that the light of mode 1 having the lowest order passes through the side closest to the surface of the surface layer, from the position of the bright line corresponding to mode 1 of the two kinds of light components, The refractive index is calculated, and the stress near the surface of the chemically strengthened glass is determined from the difference between the two types of refractive index and the photoelastic constant of the glass (see, for example, Patent Document 1).

  Further, regarding the measurement of the stress distribution of the surface layer of the chemically strengthened glass, based on the principle of the above nondestructive measurement technique, the refractive index distribution from the surface of the glass is calculated based on the positions of the bright lines corresponding to all modes, Furthermore, a method for obtaining a stress distribution based on the photoelastic effect has been proposed (for example, see Patent Document 2).

JP-A-53-136886 JP, 2016-142600, A International Publication No. 2018/056121

Yogyo-Kyokai-Shi (Ceramics Association magazine) 87 {3} 1979

  In recent years, lithium-aluminosilicate-based glass has been attracting attention as a glass that can be easily ion-exchanged and has a high surface stress value and a deep stress layer in a short time in a chemical strengthening process.

This glass was subjected to two chemical strengthening treatments, the first being soaked in hot NaNO ₃ molten salt and the second being hot KNO ₃ molten salt. , Li ions are converted to Na ions, and only in the region near the surface by the second chemical strengthening treatment, Li ions or ions once exchanged with Na ions are ion-exchanged with K ions. Since K ions have a larger ionic radius than Li ions and Na ions, a strong compressive stress is generated on the surface, and Na ions are likely to diffuse into the glass, so that a compressive stress is generated in a deep region to increase the strength of the glass. ing.

  Here, the refractive index of the glass decreases when Li ions are ion-exchanged with Na ions, and increases when Li ions are ion-exchanged with K ions. That is, the refractive index is higher in the region exchanged with K ions in the glass surface region and lower in the region exchanged with Na ions deeper than that, compared with the non-ion-exchanged region in the glass.

  Therefore, in the stress measuring device using the guided light of the surface described in the background art, the stress value of the outermost surface and the stress distribution of the surface region can be measured, but the stress distribution of the deeper region cannot be measured, It was not possible to know the depth of the stress layer and the stress distribution in the deep region. As a result, it was not possible to develop to find out the proper chemical strengthening conditions, and the quality control of manufacturing could not be performed.

  On the other hand, a stress measuring device that uses scattered light of a laser to measure the stress distribution of the chemically strengthened glass has been proposed (for example, see Patent Document 3). This stress measuring device can measure the stress inside the chemically strengthened glass regardless of the refractive index distribution.

  However, in this stress measuring device, the spot diameter of the laser determines the spatial resolution, and the value is about 10 μm. Therefore, the accuracy of the stress value is low in the region from the outermost surface of the glass to a depth of about 10 μm, and particularly in the chemically strengthened glass in which Li ions are replaced with K ions in the vicinity of the surface, the depth of the vicinity of the surface is about 10 μm. The stress value changes greatly. Therefore, the error of the stress value CS of the outermost surface, which is an important value for predicting the strength of glass, becomes large.

  In order to compensate for this defect, the stress near the surface is measured with a stress measuring device using guided light, and the deeper region is measured with a stress measuring device using this laser scattered light, and two stress distribution data are combined. However, it is also proposed to obtain the entire stress distribution.

  However, in the above proposal, it is necessary to perform the stress measurement twice using two types of stress measuring devices, which is a large-scale measurement. Further, the stress measuring device using scattered light of the laser changes the retardation with time and obtains an image in a moving image for measurement, so the total measuring time is considerably long and the cost of the measuring device is high. High, low throughput per short time. Therefore, although there is no problem when used for development, it is a heavy burden when 100% inspection is performed in production.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a highly-productive stress measurement device for chemically strengthened glass that can predict the stress distribution over the entire depth in a short time.

  This stress measuring device replaces lithium ions with potassium ions in the first region of the glass containing lithium ions from the surface to the ion concentration transition point in the depth direction, and in the second region below the ion concentration transition point, lithium ions are exchanged. A stress measurement device for chemically strengthened glass in which ions are replaced with sodium ions, wherein a light supply member for allowing light from a light source to enter the chemically strengthened glass, and light propagated in the chemically strengthened glass, A light extraction member to be emitted to the outside of the tempered glass, and two kinds of vibration included in the light emitted via the light extraction member, which vibrate in parallel and perpendicularly to the boundary surface between the chemically strengthened glass and the light extraction member. A light conversion member that converts a light component into two types of bright line arrays each having two or more bright lines, an image sensor that captures the two types of bright line arrays, and an image sensor that captures the two types of bright line arrays. Position measuring means for measuring the position of each two or more bright lines of the seed bright line array and the position of the end point of the stress distribution in the first region; and the position of the bright line measured by the position measuring means, and Stress distribution calculating means for calculating the stress distribution of the first area based on the position of the end point of the stress distribution of the first area, stress distribution of the first area calculated by the stress distribution calculating means, and measurement in advance. Stress distribution estimating means for estimating the stress distribution of the second region of the chemically strengthened glass to be measured based on the representative stress distribution of the second region of the chemically strengthened glass, and the stress distribution of the first region. And the stress distribution of the second area are combined to calculate a stress distribution of the entire first area and the second area.

  According to the disclosed technology, it is possible to provide a highly productive stress measurement device for chemically strengthened glass capable of predicting the stress distribution over the entire depth in a short time.

It is a figure which illustrates the stress measuring device which concerns on 1st Embodiment. It is an example of concentration distribution from the surface of K ion, Na ion, and Li ion in glass. 3 is an example of a refractive index distribution of the chemically strengthened glass having the ion concentration distribution of FIG. 2. It is a figure explaining a mode. It is a figure explaining the ray trace of each mode when a plurality of modes exist. It is a figure which illustrates the bright line sequence corresponding to a some mode. It is an example of a photograph of an actual bright line. It is the figure which showed the ray trace inside glass. It is a figure (the 1) explaining the method of calculating | requiring the stress distribution to an ion concentration transition point. It is a figure (the 2) explaining the method of calculating | requiring the stress distribution to an ion concentration transition point. It is an example of a typical stress distribution in the second region. It is an example of a stress measuring device capable of measuring the stress distribution of a typical second region. It is a figure explaining variation of stress distribution of the 2nd field. 6 is a flowchart illustrating a stress measuring method using the stress measuring device 1. It is a figure which illustrates the functional block of the calculating part 70 of the stress measuring device 1. It is an example of the stress distribution acquired using the stress measuring device 1.

  Hereinafter, embodiments for carrying out the invention will be described with reference to the drawings. In each drawing, the same components may be denoted by the same reference numerals, and duplicate description may be omitted.

<First Embodiment>
FIG. 1 is a diagram illustrating a stress measuring device according to the first embodiment. As shown in FIG. 1, the stress measurement device 1 includes a light source 10, a light supply member 20, a light extraction member 30, a light conversion member 40, a polarization member 50, an image sensor 60, and a calculation unit 70. Have.

  Reference numeral 200 is a chemically strengthened glass which is a measured object of the stress measuring device 1. The chemically strengthened glass 200 replaces lithium (Li) ions with potassium (K) ions in the first region of the glass containing lithium (Li) ions from the surface to the ion concentration transition point in the depth direction, and changes the ion concentration transition. The second region below the point is chemically strengthened glass in which lithium (Li) ions are replaced with sodium (Na) ions. The chemically strengthened glass 200 includes a surface layer having a refractive index distribution on the surface 210 side. Details of the chemically strengthened glass 200 will be described later in the section (About Li glass).

  The light source 10 is arranged so that the light ray L is incident on the surface layer of the chemically strengthened glass 200 from the light supply member 20. In order to utilize interference, the wavelength of the light source 10 is preferably a single wavelength that provides a simple bright and dark display.

  As the light source 10, for example, a Na lamp that can easily obtain light of a single wavelength can be used, and the wavelength in this case is 589.3 nm. A mercury lamp having a shorter wavelength than the Na lamp may be used as the light source 10, and the wavelength in this case is, for example, 365 nm which is the mercury I line. However, since the mercury lamp has many bright lines, it is preferable to use it through a bandpass filter that transmits only the 365 nm line.

  An LED (Light Emitting Diode) may be used as the light source 10. In recent years, LEDs having many wavelengths have been developed, but the spectrum width of the LEDs has a half-value width of 10 nm or more, the single wavelength property is poor, and the wavelength changes with temperature. Therefore, it is preferably used through a bandpass filter.

  When the light source 10 has a structure in which an LED is passed through a bandpass filter, it does not have a single wavelength property as compared with a Na lamp or a mercury lamp, but it is preferable in that an arbitrary wavelength from the ultraviolet region to the infrared region can be used. Since the wavelength of the light source 10 does not affect the basic principle of measurement of the stress measuring device 1, light sources other than the wavelengths illustrated above may be used.

  Further, in the chemically strengthened glass 200 which is the measured object of the stress measuring device 1, it is desirable to use a light source having a short wavelength such as 365 nm in order to measure only the shallow layer on the surface.

  The light source 10 may include a plurality of switchable light sources having different wavelengths. In this case, a light source having a suitable wavelength can be selected from a plurality of light sources included in the light source 10 according to the type of the chemically strengthened glass and used properly. This enables accurate stress measurement regardless of the type of chemically strengthened glass.

  The light supply member 20 and the light extraction member 30 are placed in a state of being in optical contact with the surface 210 of the chemically strengthened glass 200 which is the object to be measured. The light supply member 20 has a function of causing the light from the light source 10 to enter the chemically strengthened glass 200. The light extraction member 30 has a function of emitting the light propagating through the surface layer of the chemically strengthened glass 200 to the outside of the chemically strengthened glass 200.

  As the light supply member 20 and the light extraction member 30, for example, a prism made of optical glass can be used. In this case, in the surface 210 of the chemically strengthened glass 200, in order for the light rays to optically enter and exit through the prisms, the refractive index of these prisms needs to be higher than that of the chemically strengthened glass 200. Further, it is necessary to select a refractive index on the inclined surface of each prism so that the incident light and the outgoing light pass substantially vertically.

  For example, when the inclination angle of the prism is 60 ° and the refractive index of the chemically strengthened glass 200 is 1.52, the refractive index of the prism can be 1.72. As the light supply member 20 and the light extraction member 30, other members having the same function may be used instead of the prism. Further, the light supply member 20 and the light extraction member 30 may have an integrated structure. Further, in order to make stable optical contact, the refractive index of the light supply member 20 and the light extraction member 30 and the refraction of the chemically strengthened glass 200 are kept between the light supply member 20 and the light extraction member 30 and the chemically strengthened glass 200. It may be filled with a liquid (which may be in the form of gel) having a refractive index between the values.

  The image sensor 60 is arranged in the direction of the light emitted from the light extraction member 30, and the light conversion member 40 and the polarization member 50 are inserted between the light extraction member 30 and the image sensor 60.

  The light conversion member 40 has a function of converting the light beam emitted from the light extraction member 30 into a bright line array and condensing it on the image sensor 60. As the light conversion member 40, for example, a convex lens can be used, but another member having a similar function may be used.

  The polarizing member 50 is a light separating means having a function of selectively transmitting one of two kinds of light components vibrating in parallel and perpendicular to the boundary surface between the chemically strengthened glass 200 and the light extraction member 30. is there. As the polarizing member 50, for example, a polarizing plate or the like arranged in a rotatable state can be used, but another member having a similar function may be used. Here, the light component that oscillates parallel to the boundary surface between the chemically strengthened glass 200 and the light extraction member 30 is S-polarized light, and the light component that oscillates vertically is P-polarized light.

  The boundary surface between the chemically strengthened glass 200 and the light extraction member 30 is perpendicular to the emission surface of the light emitted outside the chemically strengthened glass 200 through the light extraction member 30. Therefore, in other words, the light component that oscillates perpendicularly to the emission surface of the light emitted outside the chemically strengthened glass 200 through the light extraction member 30 is S-polarized light, and the light component that oscillates in parallel is P-polarized light. May be.

  The image pickup device 60 has a function of converting light emitted from the light extraction member 30 and received via the light conversion member 40 and the polarization member 50 into an electric signal. More specifically, the image sensor 60 can convert received light into an electrical signal and output the brightness value of each of a plurality of pixels forming an image to the arithmetic unit 70 as image data. As the image pickup element 60, for example, an element such as a CCD (Charge Coupled Device) or a CMOS (Complementary Metal Oxide Semiconductor) can be used, but another element having a similar function may be used.

  The arithmetic unit 70 has a function of taking in image data from the image sensor 60 and performing image processing and numerical calculation. The calculation unit 70 may have a function other than this (for example, a function of controlling the light amount and the exposure time of the light source 10). The arithmetic unit 70 can be configured to include, for example, a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), a main memory, and the like.

  In this case, various functions of the arithmetic unit 70 can be realized by reading a program recorded in the ROM or the like into the main memory and executing the program by the CPU. The CPU of the arithmetic unit 70 can read and store data from the RAM as needed. However, part or all of the arithmetic unit 70 may be realized only by hardware. Further, the arithmetic unit 70 may be physically composed of a plurality of devices or the like. As the calculation unit 70, for example, a personal computer can be used.

  In the stress measuring device 1, the light ray L that has entered the surface layer of the chemically strengthened glass 200 from the light source 10 through the light supply member 20 propagates in the surface layer. Then, when the light ray L propagates in the surface layer, a mode is generated by the optical waveguide effect, travels through some predetermined paths, and is extracted to the outside of the chemically strengthened glass 200 by the light extraction member 30.

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

  With such a configuration, in the stress measuring device 1, the refractive indices of the P-polarized light and the S-polarized light in the depth direction from the surface of the surface layer of the chemically strengthened glass 200 are determined based on the positions of the bright lines of the P-polarized light and the S-polarized light. The distribution can be calculated. Further, the stress distribution in the depth direction from the surface of the surface layer of the chemically strengthened glass 200 is calculated based on the calculated difference in refractive index distribution between the P polarized light and the S polarized light and the photoelastic constant of the chemically strengthened glass 200. can do.

  Hereinafter, the measurement of the refractive index distribution and the measurement of the stress distribution in the stress measuring device 1 will be described in more detail.

(About Li glass)
Chemically strengthened glass 200 (that is, glass containing Li ions in the first region from the surface to the ion concentration transition point in the depth direction to replace the Li ions with K ions in the first region of the glass including Li ions). In the second region below the concentration transition point, the chemically strengthened glass in which Li ions are replaced with Na ions) will be described in detail.

  FIG. 2 shows an example of the concentration distribution of K ions, Na ions, and Li ions in the glass from the surface. In the reinforcing layer, Li ions are replaced with K ions near the surface layer, and Li ions are replaced with Na ions in a deeper region. The depth A in FIG. 2 is the depth at which the ion concentration shifts from the region where the K ions are dominant to the region where the Na ions are dominant, and is the ion concentration transition point.

  The respective ionic radii are Li <Na <K, with Li being the smallest and K being the largest. Therefore, a strong compressive stress is generated near the surface, which is replaced with K ions near the surface, and a relatively weak compressive stress is generated, in a region deeper than Na and replaced with Na. Further, since Na ions are more likely to diffuse than K ions, they are replaced to a deeper region, and as a result, a very strong compressive stress can be generated near the surface and a relatively weak compressive stress can be generated to a very deep region. Can be generated.

Such an ion concentration distribution is obtained by performing a chemical strengthening process in which the molten salt of NaNO ₃ is divided into two, the molten salt of KNO ₃ is divided into two, the first time, and the first time, at a relatively low temperature for a long time. The second time can be obtained by performing a chemical strengthening process at a high temperature for a short time.

Further, it is possible to obtain it in a single chemical strengthening step by using a molten salt obtained by mixing NaNO ₃ and KNO ₃ .

FIG. 3 is an example of the refractive index distribution of the chemically strengthened glass having the ion concentration distribution of FIG.
With respect to Li ions, K ions have a high refractive index, and Na ions have a low refractive index. Therefore, as shown in FIG. 3, the refractive index increases from the ion concentration transition point A toward the surface and from the ion concentration transition point A toward the inside of the glass, and the refractive index becomes lowest at the ion concentration transition point A.

  Next, the measurement of the refractive index distribution and the measurement of the stress distribution in the stress measuring device 1 will be described in detail.

(Mode and bright line)
First, with reference to FIG. 4 and FIG. 5, the trajectory and mode of a light beam when the light beam is incident on the surface layer of the chemically strengthened glass 200 will be described.

  In FIG. 4, the chemically strengthened glass 200 has a refractive index distribution from the surface 210 in the depth direction. In FIG. 4, assuming that the depth from the surface 210 is x and the refractive index distribution in the depth direction is n (x), the refractive index distribution n (x) in the depth direction is the curve shown in FIG. 3 described above. become that way. Consider from the surface to the ion concentration transition point A in this refractive index curve.

  In the first region from the surface to the ion concentration transition point A, the refractive index becomes lower as it goes inward. Therefore, in FIG. 4, the light ray L incident on the surface 210 at a shallow angle (in the example of FIG. 4, is incident through the light supply member 20 having a refractive index larger than that of the chemically strengthened glass 200). The locus gradually approaches parallel to the surface 210 and reverses from the depth direction to the direction of the surface 210 at the deepest point xt. Then, the light rays whose ray trajectories are inverted travel toward the surface 210 in a shape similar to the shape of the ray trajectories from the point of incidence to the point of inversion, at least a part of which is reflected by the surface 210, and the inside of the chemically strengthened glass 200 is again seen. Go to. Then, the light ray that has proceeded to the inside of the chemically strengthened glass 200 again passes through the same trajectory as the trajectory of the light ray up to that point, is inverted at the depth xt and returns to the surface 210, and this is repeated. Going back and forth with xt. Then, since the light travels from the surface 210 in a limited space having a width xt, the light can propagate only as a discrete mode having a finite value.

  That is, only a plurality of light rays having a certain fixed path can propagate through the surface layer of the chemically strengthened glass 200. This phenomenon is called the optical waveguide effect, which is also the principle by which a light ray travels in an optical fiber. The mode of light that propagates through the surface 210 due to the optical waveguide effect and the ray trajectory of that mode are determined by the refractive index distribution in the depth direction from the surface 210.

  However, when the depth of the ion concentration transition point A is reached before reversal due to the angle of incidence of the incident light ray L, the refractive index distribution is reversed in the region further than that, so it cannot be reversed, and Go deeper. That is, the guided light is obtained in the first region having a depth from the surface to the ion concentration transition point A. The boundary at the incident angle is the same as the critical angle of the refractive index at the ion concentration transition point A. After this, the guided light obtained in the first region having a depth from the surface to the ion concentration transition point A will be described.

  FIG. 5 is a diagram illustrating a ray trace of each mode in the case where a plurality of modes exist in the first region at the depth from the surface to the ion concentration transition point A. In the example of FIG. 5, three modes of mode 1, mode 2, and mode 3 are shown, but higher-order modes may be included.

  The mode 1 having the lowest order has the shallowest angle with respect to the surface 210 when the ray trajectory is reflected by the surface 210 (the smallest exit margin). Further, the deepest point of the ray trace is different for each mode, and the deepest point xt1 in mode 1 is the shallowest. As the order of the modes increases, the angle formed by the surface 210 with respect to the surface 210 increases (the emission complementary angle increases). The deepest point xt2 in mode 2 is deeper than the deepest point xt1 in mode 1, and the deepest point xt3 in mode 3 is deeper than the deepest point xt2 in mode 2. However, there is no mode in which the deepest point is deeper than the depth of the ion concentration transition point A.

  Here, the incident angle of the light ray with respect to the predetermined surface is the angle formed by the incident light ray and the normal line of the predetermined surface. In contrast, the incident angle of incidence of a light ray on a predetermined surface is the angle formed by the incident light ray and the predetermined surface. That is, if the incident angle of the light ray on the predetermined surface is θ, the incident angle of incidence of the light ray on the predetermined surface is π / 2−θ. The same applies to the relationship between the emission angle and the emission complementary angle of a light ray with respect to a predetermined surface.

  Although the incident light is represented by one light beam in FIG. 5, the incident light has a certain spread. The light having the spread has the same complementary angle of the light emitted from the surface 210 in the same mode. Since the lights other than the generated modes cancel each other out, the lights other than the lights corresponding to the respective modes are not emitted from the surface 210.

  Further, in FIG. 1, the light supply member 20, the light extraction member 30, and the chemically strengthened glass 200 have the same shape in the depth direction. Therefore, the light condensed by the light conversion member 40 is imaged on the image pickup element 60, which is the focal plane of the light conversion member 40, as a bright line in the depth direction corresponding to the mode.

  Then, since the emission complementary angle is different for each mode, as shown in FIG. 6, the bright lines are sequentially arranged for each mode to form a bright line row. The bright line array is usually a bright line array, but when the light supply member 20 and the light extraction member 30 in FIG. 1 are in contact with each other and integrated, the direct light from the light source is used as the reference light for the emitted light. It may also act as a dark line. However, the position of each line is exactly the same regardless of whether it is a row of bright lines or a row of dark lines.

  Thus, the bright line appears as a bright line or a dark line when the mode is established. Even if the interference color of the bright line changes depending on the brightness of the reference light, it has no effect on the calculation of the refractive index distribution and the stress distribution according to the present embodiment. Therefore, in the present application, bright lines and dark lines are referred to as bright lines for convenience.

  By the way, the exit angle when the light ray propagated in the surface layer is refracted and is emitted to the outside of the chemically strengthened glass 200, the emission complementary angle of the chemically strengthened glass 200 at the deepest point of the ray trajectory of the light ray in the surface layer. It is equal to that of the critical refraction light when a medium having a refractive index, that is, a refractive index equal to the effective refractive index nn is in contact with the light extraction member 30. The deepest point in each mode can also be interpreted as the point at which the light rays in that mode are totally reflected.

  In addition, since all the light that is incident at an angle larger than the output complementary angle that is the depth of the ion concentration transition point A does not return to the glass surface, there is no light from the light extraction member 30 and it becomes dark. From this position, the refractive index at the ion concentration transition point A can also be known.

  FIG. 7 is an example of a photograph of an actual bright line. In FIG. 7, the upper half is a P-polarized bright line image of the two light components, and the lower half is an S-polarized bright line image. The P-polarized light is vertical to the surface of the chemically strengthened glass 200, and the S-polarized light is horizontal. This is a photograph when it becomes a dark line of the bright line, but in each of the P-polarized light and the S-polarized light, a portion where the brightness becomes dark at the ion concentration transition point A appears at the end of the bright line sequence. This point is the critical point.

  Here, the relationship between the difference Δn in the effective refractive index nn between certain modes and the distance ΔS between the bright lines is as follows: the focal length f of the light conversion member 40, the refractive index np of the light extraction member 30, the refractive index of the chemically strengthened glass 200. If ng is set, there is a relationship of the following formula (1) and formula (2).

Therefore, if the position of the effective refractive index at one point on the image sensor 60 is known, the effective refractive index of each mode corresponding to the bright line from the position of the observed bright line, that is, in the surface layer of the chemically strengthened glass 200. The refractive index at the deepest point of the ray trace of can be obtained. Also, the refractive index at the ion concentration transition point A can be obtained from the position where the brightness changes.

(Calculation of refractive index distribution)
In the present embodiment, the refractive index distribution is calculated using the following formula (3). The formula (3) is derived by the inventors based on the technical information and the like described in Non-Patent Document 1. In Non-Patent Document 1, it is assumed that the refractive index distribution changes linearly, and the light traveling path is approximated to an arc. On the other hand, in the present embodiment, the refractive index distribution is set to an arbitrary distribution n (x) in order to obtain the condition that the mode is satisfied in the arbitrary refractive index distribution.

  In the equation (3), θ is the exit angle of the light ray that travels in a straight line through the minute distance dr, n0 is the refractive index of the surface of the chemically strengthened glass, Θ is the exit angle of the ray that has entered the chemically strengthened glass, and λ is the chemical strengthening. The wavelength of the light beam incident on the glass, N is the order of the mode (for example, N = 1 for mode 1). Further, G1 is a point at which the light beam is incident on the chemically strengthened glass, F2 is a deepest point (xt) at which the light beam is inverted, and G2 is a point at which the light beam inverted at F2 reaches the chemically strengthened glass again, which is different for each mode. The first term on the left side is a term relating to light propagating in the surface layer, and the second term on the left side is a term relating to light virtually propagating on the surface 210.

Using the formula (3), it is assumed that the rate of change of the refractive index of the chemically strengthened glass 200 is constant between the deepest points of the modes of which the orders are adjacent to each other. The depth of the points can be calculated and the overall refractive index distribution can be determined.

  For example, in FIG. 5, the refractive indices of the surface layers at the depths of the deepest parts xt1, xt2, xt3 ... In each mode, that is, the effective refractive indices are n1, n2, n3. Further, it is assumed that the refractive index change rates of the surfaces 210-xt1, xt1-xt2, xt2-xt3, ... Are linear, and the refractive index change rates are α1, α2, α3 ,. To do.

  Since the ray trajectory in a certain mode n passes through a portion shallower than the deepest point xtn of that mode, if the refractive index distribution from the surface to xtn is determined, the ray trajectory in that mode n is uniquely determined. If xt of all modes is known, the refractive index distribution is uniquely determined, but from equation (3), not only analytically, but also in numerical calculation, the refractive index distribution can be directly obtained at once. It is difficult.

  Therefore, first, α1, α2, and xt1, xt2 are obtained using modes 1 and 2 that pass through the portion closest to the surface 210. Then, in mode 3, since xt1 and xt2 are known and the only unknown parameter is xt3, xt3 can be easily obtained. Similarly, if xt4, xt5 ... Are obtained in order for modes 4, 5, ..., The deepest point xtn corresponding to all modes can be obtained. Then, the refractive index distribution in the depth direction can be obtained from the surface 210.

  FIG. 8 is a diagram showing a ray trace inside the glass. A specific method of calculating the refractive index distribution will be described with reference to FIG. First, the ray tracing method is used to find the left side of equation (3). In FIG. 8, the x direction (longitudinal direction) is the depth direction of the chemically strengthened glass 200, and the y direction (horizontal direction) is the direction horizontal to the surface 210 of the chemically strengthened glass 200. Further, the refractive index at the depth x is n (x). Note that H is a normal line to the surface 210.

  Now, let us consider the light ray L that is incident on the surface 210 from the light supply member 20 at the incident complementary angle Ψ with the refractive index of the light supply member 20 being 1.72. The coordinates of the incident point are (x0, y0). Note that x0 = 0. At this time, the light ray L incident on the inside of the chemically strengthened glass 200 is refracted and advances at the exit complementary angle θ1. At this time, the Snell's equation holds for Ψ and θ1.

  Next, the locus of the light ray L is a curve inside the chemically strengthened glass 200, but it is assumed that a certain minute distance dr advances in a straight line (the distance dr is preferably about 1/10 to 1/100 of the wavelength). That is, it is assumed that the light ray travels in a straight line in the direction of the output complementary angle θ1 by dr. At this time, the movement amount in the x direction is dx1 = dr · sin θ1, and the movement amount in the y direction is dy1 = dr · cos θ1. The coordinates of the moved point are (x1, y1) = (dr · sin θ1, y0 + dr · cos θ1).

  The refractive index at the starting point coordinates (x0 = 0, y0) of this partial ray trajectory is n (0), and the refractive index at the ending point coordinates (x1, y1) is n (x1). In the locus, the refractive index at the starting point is constant, and the refractive index changes to n (x1) at the ending point. Then, the next ray trajectory changes its angle to the exit complementary angle θ2 according to Snell's law. The light that travels at the exit complementary angle θ2 travels in a straight line by dr, and further travels while changing the direction to the exit complementary angle θ3 (not shown). This is repeated to find the entire ray trajectory by following the ray trajectory.

At this time, the first term on the left side of the equation (3) is calculated each time the dr is advanced. For example, in the portion from the coordinates (x0 = 0, y0) to the coordinates (x1, y1), the first term is dr · cos θ1 · n (0), which can be easily calculated. Other dr can be calculated in the same manner. Then, when the first term obtained for each dr is added until the ray trajectory returns to the surface 210, all the first terms on the left side of the equation (3) are obtained. At this time, the distance Σdy of the ray trajectory in the y direction can be known. Since d _G1G2 = Σdy and Θ = θ1 in Expression (3), the second term on the left side of Expression (3) is obtained, and all the left sides of Expression (3) are obtained.

  Next, a method of calculating the refractive index distribution will be described. First, as shown in Non-Patent Document 1, the refractive index of the surface 210 and the deepest point of Mode 2 are obtained from the positions of the bright lines of Mode 1 and Mode 2. Thereby, the values of the three points, the surface 210 (x = 0), the deepest point (xt1) of mode 1 and the deepest point (xt2) of mode 2, and the refractive indices n0, n1 and n2 at that point can be known. However, since the surface is an extrapolation of mode 1 and mode 2, these three points are straight lines.

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

  After that, xt3 can be easily obtained by using a non-linear equation calculation method such as the bisection method or Newton method with xt3 as a parameter. Then, when up to xt3 is obtained, xt4 is obtained from the bright line position of the next mode 4, and the same calculation is repeated for all the bright lines, whereby the entire refractive index distribution can be calculated.

(Calculation of stress distribution)
Since the chemically strengthened glass has a strong in-plane compressive stress, the refractive index of P-polarized light and the refractive index of S-polarized light are deviated by the stress due to the photoelastic effect. That is, when in-plane stress is present on the surface 210 of the chemically strengthened glass 200, the P-polarized light and the S-polarized light have different refractive index distributions, different modes of generation, and different positions of bright lines.

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

Specifically, the stress distribution can be calculated using the following equation (4). In the equation (4), kc is a photoelastic constant, and Δn _PS (x) is a difference in refractive index distribution between P-polarized light and S-polarized light. Since P refractive index of the polarization distribution n _{P (x)} and S-polarized light of the refractive index distribution n _{S (x)} is obtained, respectively discretely or linearly approximated between the respective points, approximation using a plurality of points By calculating the curve, the stress distribution can be obtained at any position.

By extrapolating the approximated straight line or curve to the refractive index at the critical point in FIG. 7, that is, the refractive index at the ion concentration transition point A, the first region from the surface to the ion concentration transition point A is extrapolated. It is possible to know the refractive index distribution and the stress distribution.

  That is, the position of the end point (critical point) of the stress distribution in the first region can be obtained by extrapolating the stress distribution calculated based on the position of the bright line up to the refractive index position of the ion concentration transition point A.

  A method for obtaining the stress distribution up to the ion concentration transition point A will be specifically described with reference to FIGS. 9 and 10. FIG. 9 is a diagram schematically showing images of bright lines in two light components, and there is a boundary with a dark part on the right side of the bright line row. This boundary is the critical point. The upper half is the bright line for the P-polarized light of the two light components, and the lower half is the bright line for the S-polarized light.

  In the example of FIG. 9, there are four bright lines each. FIG. 10 shows the depth and effective refractive index for each bright line calculated from this bright line array, that is, the depth of the deepest point of the ray trajectory in that mode and the refractive index at that depth. The bright lines for P-polarized light and S-polarized light are indicated by Δ and ◯. These points are shown by solid lines for the P-polarized light and the S-polarized light, respectively, and the curves obtained by calculating the approximate function of the quadratic curve by the least-squares method.

  On the other hand, also at the position of the boundary indicating the critical point in FIG. 9, the refractive index can be obtained from the position similarly to the bright line. The refractive index at the critical point on each of the two curves is indicated by ▽ and □. This critical point is the ion concentration transition point A as described above. Therefore, the depths of ▽ and □ are the depths of the ion concentration transition point A, and for both P-polarized light and S-polarized light, the curves from the surface of each approximate curve in FIG. Are the refractive index distributions of the first region from the surface to the ion concentration transition point A in the depth direction.

  Furthermore, the stress distribution from the surface to the ion concentration transition point A can be obtained from the difference between these two curves and the photoelastic constant of the chemically strengthened glass.

  As described above, the position of the end point (critical point) of the stress distribution in the first region can be obtained by extrapolating the stress distribution calculated based on the position of the bright line to the refractive index position at the ion concentration transition point.

  Further, the stress distribution in the first region may be obtained as follows. That is, the effective refractive index at the critical points of P-polarized light and S-polarized light is the refractive index at the depth of the ion concentration transition point A for each light component. Since the difference in the refractive index is due to the stress at the ion concentration transition point A, the stress at the ion concentration transition point A can be obtained from the photoelastic constant. The stress distribution is calculated from the difference between the above two quadratic curves and the photoelastic constant, and the stress distribution curve from the surface to the stress value at the ion concentration transition point A obtained from the difference between the two boundaries is the first region. May be the stress distribution.

  In this way, the position of the end point (critical point) of the stress distribution in the first region is calculated from the stress distribution calculated from the position of the bright line, from the refractive index difference and the photoelastic constant at the ion concentration transition points of the two types of light components. It can also be obtained by extrapolating to the obtained stress value.

  Although a quadratic function is used as an approximate curve in the description here, a higher-order power polynomial, an error function, or a linear function may be used.

As described above, by using the stress measuring device 1, it is possible to measure the stress distribution in the first region in which the Li ions are replaced by the K ions and from the surface to the ion concentration transition point A in the depth direction. is there.
(Measurement of stress in the second region below the ion concentration transition point A)
Next, a method of estimating the stress distribution in the second region at the ion concentration transition point A or deeper, that is, the region in which Li ions are replaced by Na ions, using the stress measuring device 1, will be described.

  FIG. 11 shows that the same glass is chemically strengthened in advance under the same conditions as in the first chemical strengthening step, and the stress distribution is measured immediately after that. An example of a typical stress distribution in the second region is shown. Is.

  The stress distribution of the typical second region can be measured using, for example, the stress measuring device 2 shown in FIG. As shown in FIG. 12, the stress measurement device 2 includes a laser light source 110, a polarization member 120, a polarization phase difference variable member 130, a light supply member 140, a light conversion member 150, an image sensor 160, and a calculation unit. 170 and a light wavelength selection member 180. The stress measuring device 1 may have a stress measuring unit including the structure of the stress measuring device 2. That is, the stress measuring device 1 may have the function of the stress measuring device 2.

  The laser light source 110 is a semiconductor laser or the like, and is arranged so that the laser light L is incident on the surface layer of the chemically strengthened glass 200 from the light supply member 140.

  The polarization member 120 is inserted between the laser light source 110 and the polarization phase difference variable member 130 as needed. Specifically, when the laser light L emitted from the laser light source 110 is not polarized, the polarization member 120 is inserted between the laser light source 110 and the polarization phase difference variable member 130. When the laser light L emitted from the laser light source 110 is polarized light, the polarization member 120 may or may not be inserted.

  The polarization phase difference variable member 130 is inserted between the laser light source 110 and the light supply member 140, and has a function of changing the polarization phase difference of the laser light by one wavelength or more with respect to the wavelength of the laser light.

  The light supply member 140 is placed in a state of being in optical contact with the surface 210 of the chemically strengthened glass 200. The light supply member 140 has a function of causing the light from the laser light source 110 to enter the chemically strengthened glass 200, and for example, a prism made of optical glass can be used.

  The image sensor 160 has a function of capturing a plurality of images of scattered light generated when the laser light whose polarization phase difference is changed is incident on the chemically strengthened glass at predetermined time intervals and acquiring a plurality of images.

  The light conversion member 150 is a lens that is inserted between the image sensor 160 and the laser beam L so as to form an image of the scattered light LS of the laser beam L on the image sensor 160.

  The calculation unit 170 measures the periodic brightness change of scattered light using a plurality of images, calculates the phase change of the brightness change, and calculates the stress distribution in the depth direction from the surface of the chemically strengthened glass based on the phase change. It has a function to calculate.

  An optical wavelength selection member 180 such as a bandpass filter or a shortpass filter having a multilayered dielectric film may be inserted between the laser light L and the image sensor 160. By inserting the light wavelength selection member 180, fluorescent light and extraneous light generated from the laser light L can be removed, and only the scattered light LS can be collected in the imaging element 160.

  As described above, the stress measuring device 2 is a stress measuring device that uses scattered light of a laser, and the accuracy is poor near the surface and the entire stress cannot be accurately measured. The stress in the two regions can be accurately measured. Details of the stress measuring device 2 are described in Patent Document 3.

  When measuring the stress distribution of this typical second region, it is recommended to take out a plurality of samples, measure and average the stress distribution in consideration of variations in glass composition and chemical strengthening process and unevenness. desirable.

  As a method of averaging, the stress values for each depth of the distribution data are averaged to obtain an average stress distribution of the whole, which can be used as a representative stress distribution of the second region.

Usually, the stress distribution in the chemical strengthening step is formed by diffusion of K ions and Na ions, so the stress distribution St _tm can be expressed by a combination of the error function and the constant of the equation (5). In the equation (5), x is the depth from the surface, and the constant term A5 is a term because the stress distribution is shifted to the tensile stress side in order to balance the stress in the entire glass.

Using the equation (5), the stress distribution in the representative second region is calculated by the least squares method, and the approximate function is obtained.

  Further, as another method of averaging the stress distribution, the average of the distribution can be obtained from the average of the coefficients of the approximate function of the stress distribution measured.

  Further, in the distribution data, the values of peculiar points, for example, the value of the glass surface, the point of 100 μm in depth, the glass midpoint, or the point where the stress becomes 0, are averaged, and the entire distribution is restored by a function. An average stress distribution can also be used. Further, as a typical stress distribution, a median value, a mode value, etc. may be used instead of the average value.

The average stress distribution function obtained here is a typical stress distribution, and in fact, the composition of the glass varies, the nonuniformity of the temperature of the molten salt of KNO ₃ or NaNO ₃ which is the chemical strengthening solution, Deterioration of the glass, non-uniformity of circulation, etc. cause differences in the degree of strengthening of each glass. Therefore, it is necessary to predict the stress distribution in the second region of each glass based on the typical stress distribution function.

  First, a correction function ks is introduced into a function of stress considering the degree of strengthening and variation, and equation (5) is modified to assume equation (6).

However, in Expression (6), A3 and A4 are coefficients when the representative stress distribution of the second region is expressed by an approximate function. Further, in Expression (6), ks and Am5 are coefficients calculated under the condition that the stress distribution is satisfied in the first region, passing through the end point of the stress distribution.

  More specifically, ks is a correction coefficient for the degree of reinforcement and variation. FIG. 13 shows the difference in stress distribution when ks = 0.8 and 1.0.1.2. When ks = 1, the solid line is shown in the example of FIG. 13, the same as the equation (5), and a typical stress distribution is obtained. When ks <1, in the example of FIG. 13, ks = 0.8, which is indicated by a short broken line. This is when the degree of strengthening is low, for example, when the chemical strengthening liquid is deteriorated or the temperature is low. When ks> 1, in the example of FIG. 13, ks = 1.2. This is when the degree of strengthening is strong, for example, when the strengthening temperature is high.

Am5 is a term that balances the stress as a whole. This correction coefficient can be determined by the thickness of each glass, the stress distribution measured in the stress measuring device 1 in the first region from the surface to the ion concentration transition point A, and the glass thickness. That is, the stress distribution in the second region at the ion concentration transition point A and deeper can be known.
(Correction method for the second region deeper than the ion concentration transition point A)
The stress distribution estimating unit 73, which will be described later, for example, expresses the stress distribution in the typical second region of the chemically strengthened glass by an approximate function, and satisfies the stress balance by passing through the end point of the stress distribution in the first region. Thus, the stress distribution of the second region can be estimated by obtaining the coefficient of the approximate function. This will be described in detail below.

  Consider the following two conditions (condition 1 and condition 2) in order to obtain the correction coefficients ks and Am5. Condition 1: The stress distribution in the second region below the ion concentration transition point A expressed by the equation (6) passes through the end point of the stress distribution in the first region measured previously. Condition 2: The integrated value of the stress distribution from the surface to the glass midpoint (point at a depth of 1/2 of the glass thickness) becomes 0 (stress balance can be obtained) from the stress balance.

  The value of the end point of the data measured by the stress measuring device 1, that is, the depth and the stress value corresponding to the ion concentration transition point A are xtp and ytp, and the condition 1 is represented by the formula (7). When 2 is represented by a formula, it becomes like a formula (8).

S _fsm is an integrated value of stress in the first region from the surface to the ion concentration transition point A, and can be obtained by numerically integrating the stress part data measured by the stress measuring device 1.

  Then, since it becomes a binary simultaneous equation with two unknowns ks and Am5, the range of the solution can be easily predicted. For example, a numerical integration is used for integration, and a numerical solution of an equation such as a dichotomy method or a pinching method can be easily obtained as a numerical solution. Also, since there is no derivative, the Newton's method can be used as a solution by using numerical differentiation for the derivative.

  The function obtained by applying the solutions ks and Am5 obtained by these numerical analysis methods to the equation (2) becomes the stress distribution in the second region at the ion concentration transition point A or deeper of each glass.

  From this result, the first region from the surface to the ion concentration transition point A is the stress distribution measured by the stress measuring device 1, and the stress distribution in the second region below the ion concentration transition point A is the estimated stress distribution obtained from this solution. The total stress distribution can be obtained by combining both.

  It is also possible to obtain the entire stress distribution by making the stress distribution in the vicinity of the surface of the stress measuring device 1 into an approximate function with an error function and performing synthesis with the function.

  Further, by expanding the expression (6) into the expression (9), it is possible to perform prediction with higher accuracy. kp is a value obtained experimentally and is a numerical value of 0.3 or more and 0.8 or less. kp is a coefficient determined by the composition of the glass and the chemical strengthening step, and the stress distribution in the second region can be more accurately predicted by experimentally obtaining kp.

(Measurement flow)
FIG. 14 is a flowchart illustrating a stress measuring method using the stress measuring device 1. FIG. 15 is a diagram illustrating functional blocks of the calculation unit 70 of the stress measurement device 1.

  First, in step S501, light from the light source 10 is made to enter the chemically strengthened glass 200 (light supply step). Next, in step S502, the light propagating in the chemically strengthened glass 200 is emitted to the outside of the chemically strengthened glass 200 via the light extraction member 30 (light extraction step).

  Next, in step S503, the light conversion member 40 and the polarization member 50 are parallel and perpendicular to the boundary surface between the chemically strengthened glass 200 and the light extraction member 30, which is included in the light emitted to the outside of the chemically strengthened glass 200. The two kinds of light components (P-polarized light and S-polarized light) that vibrate in the direction are converted into two kinds of bright line arrays each having two or more bright lines (light conversion step).

  Next, in step S504, the image sensor 60 images the two types of bright line arrays converted in the light conversion process (imaging process). Next, in step S505, the position measuring means 71 of the calculation unit 70 measures the positions of two or more bright lines in each of the two types of bright line arrays and the position of the critical point from the image obtained in the imaging step. (Position measurement process).

  Next, in step S506, the stress distribution calculation means 72 of the calculation unit 70 calculates the stress distribution in the first region based on the positions of the bright lines and the positions of the critical points measured in the position measuring step (stress distribution). Calculation process).

  In steps S505 and S506, all the bright lines in the bright line sequence imaged in the imaging process can be used, but some of the bright lines in the bright line sequence imaged in the imaging process may be used. .. For example, if the two kinds of bright line arrays obtained in the imaging step each have four bright lines, even if all four bright lines are used for each of the two kinds of bright line arrays in steps S505 and S506. Alternatively, three or two of the four bright lines may be used.

  Next, in step S507, the stress distribution estimation unit 73 of the calculation unit 70 causes the stress distribution in the first region calculated in the stress distribution calculation step and the stress distribution in the second region representative of the chemically strengthened glass measured in advance, Based on, the stress distribution in the second region of the chemically strengthened glass to be measured is estimated (stress distribution estimation step). The specific estimation method is as described above.

  Next, in step S508, the synthesizing unit 74 of the computing unit 70 synthesizes the stress distribution of the first region and the stress distribution of the second region to calculate the overall stress distribution of the first region and the second region ( Synthesis process). For example, the stress distribution shown in FIG. 16 can be obtained. In FIG. 16, the solid line portion is the stress distribution in the first region (region from the surface to the ion concentration transition point A in the depth direction), and is the portion calculated in step S506. Also, the broken line portion is the stress distribution in the second region (region deeper than the ion concentration transition point A), and is the portion estimated in step S507.

  In this way, the stress measuring device 1 calculates the stress distribution of the first region from the surface to the ion concentration transition point A in the depth direction, and at the same time, calculates the stress distribution of the second region deeper than the ion concentration transition point A in advance. It is estimated based on the measured stress distribution in the representative second region of the chemically strengthened glass. This eliminates the need to measure the stress distribution in the second region in the process of manufacturing the chemically strengthened glass, so that the stress distribution in the entire depth can be predicted in a short time. That is, the stress measuring device 1 is a stress measuring device for chemically strengthened glass with high productivity capable of predicting stress distribution over the entire depth in a short time. Since the measurement time of the first region is usually about several seconds and the measurement time of the second region is about several tens of seconds, the productivity improving effect by not measuring the stress distribution in the second region is great.

  The stress measuring method using the stress measuring device 1 can be applied to the chemically strengthened glass to be measured and the previously measured chemically strengthened glass when the glass composition and the chemical strengthening conditions are not significantly different. Especially when the data of a large amount of chemically strengthened glass produced under equivalent conditions can be acquired in advance, when the stress distribution changes due to deterioration of the strengthening salt, non-uniformity, temperature accuracy, glass composition accuracy, etc. Even in such cases, the stress distribution of the entire chemically strengthened glass to be measured can be accurately acquired.

  If the chemically strengthened glass to be measured and the chemically strengthened glass measured in advance have significantly different glass compositions and chemical strengthening conditions, correction based on one representative second region stress distribution Then, there are cases where sufficient accuracy cannot be obtained. In such a case, it is possible to measure the stress distribution with higher accuracy by preparing and using a plurality of typical stress distributions of the second region for each condition.

  Further, the light source 10 may include a plurality of switchable light sources having different wavelengths. In this case, the light source 10 is switched to a plurality of different wavelengths, the positions of the bright lines at the different wavelengths are measured, the stress distributions measured at the respective wavelengths are calculated from the measured positions of the bright lines, and the results are synthesized. A more accurate stress distribution can be obtained.

  The preferred embodiments and examples have been described in detail above, but the embodiments and examples are not limited to the above-described embodiments and examples, and the embodiments described above are not deviated from the scope of the claims. And various modifications and substitutions can be added to the embodiment.

  For example, in each of the above-described embodiments, the light source is described as a constituent element of the stress measuring device, but the stress measuring device may have a structure without a light source. In this case, the stress measurement device can be configured to include, for example, the light supply member 20, the light extraction member 30, the light conversion member 40, the polarization member 50, the imaging element 60, and the calculation unit 70. .. The light source can be used by the user of the stress measuring device by preparing an appropriate one.

  Further, it is also possible to adopt a configuration in which two types of light components (P-polarized light and S-polarized light) are incident on the light supply member 20. In this case, it is not necessary to dispose the polarization member 50 on the optical path from the light extraction member 30 to the image pickup element 60.

1, 2 Stress Measuring Device 10 Light Source 20 Light Supply Member 30 Light Extracting Member 40 Light Converting Member 50 Polarizing Member 60 Imaging Device 70 Computing Unit 71 Position Measuring Means 72 Stress Distribution Calculating Means 73 Stress Distribution Estimating Means 74 Synthetic Means 110 Laser Light Sources 120 Polarization member 130 Polarization phase difference variable member 140 Light supply member 150 Light conversion member 160 Image sensor 170 Calculation unit 180 Light wavelength selection member 200 Chemically tempered glass 210 Surface of chemically tempered glass

Claims (8)

In the first region of the glass containing lithium ions from the surface to the ion concentration transition point in the depth direction, lithium ions are replaced with potassium ions, and in the second region below the ion concentration transition point, lithium ions are replaced with sodium ions. A stress measurement device for chemically strengthened glass,
In the chemically strengthened glass, a light supply member for making light from a light source incident,
Light propagating in the chemically strengthened glass, a light extraction member for emitting to the outside of the chemically strengthened glass,
Two or more bright lines, which are included in the light emitted through the light extraction member, vibrate in parallel and perpendicular to the boundary surface between the chemically strengthened glass and the light extraction member. A light conversion member for converting into two kinds of bright line arrays having
An image sensor for capturing the two kinds of bright line arrays,
Position measuring means for measuring the positions of two or more bright lines of each of the two types of bright line arrays and the position of the end point of the stress distribution of the first region from the image obtained by the image sensor,
A stress distribution calculating means for calculating the stress distribution of the first area based on the position of the bright line measured by the position measuring means and the position of the end point of the stress distribution of the first area;
The second region of the chemically strengthened glass to be measured is based on the stress distribution of the first region calculated by the stress distribution calculation means and the stress distribution of the representative second region of the chemically strengthened glass measured in advance. Stress distribution estimating means for estimating the stress distribution of
A stress measurement, comprising: a synthesizing unit that synthesizes the stress distribution of the first region and the stress distribution of the second region to calculate the stress distribution of the entire first region and the second region. apparatus.   The stress distribution estimating means expresses a stress distribution in a typical second region of the chemically strengthened glass with an approximate function, passes through the end point of the stress distribution in the first region, and satisfies the stress balance. The stress measuring device according to claim 1, wherein the stress distribution of the second region is estimated by obtaining a coefficient of an approximate function. The stress measuring device according to claim 2, wherein the approximation function is the following formula (9).
However, in the equation (9), A3 and A4 are coefficients when the representative stress distribution of the second region in claim 2 is expressed by an approximate function,
ks and Am5 are coefficients that are calculated under the condition that the stress distribution in claim 2 is passed and the stress is balanced.
kp is a numerical value of 0.3 or more and 0.8 or less, which is an experimentally obtained value.   The end point of the stress distribution of the first region is obtained by extrapolating the stress distribution calculated based on the position of the bright line to the refractive index position of the ion concentration transition point. The stress measuring device according to any one of claims.   The end point of the stress distribution of the first region is the stress distribution calculated from the position of the bright line outside the stress value obtained from the refractive index difference at the ion concentration transition point and the photoelastic constant in the two light components. It obtains by inserting, The stress measuring device as described in any one of Claim 1 thru | or 3 characterized by the above-mentioned. A stress measuring unit for measuring a stress distribution in a typical second region of the chemically strengthened glass,
The stress measurement unit,
A polarization phase difference variable member for changing the polarization phase difference of the laser light by one wavelength or more with respect to the wavelength of the laser light;
The scattered light emitted by the laser light having a variable polarization phase difference is incident on the chemically strengthened glass, imaged a plurality of times at a predetermined time interval, and an imaging element that acquires a plurality of images,
Using the plurality of images to measure the periodic brightness change of the scattered light, calculate the phase change of the brightness change, the stress distribution in the depth direction from the surface of the chemically strengthened glass based on the phase change. The calculation part which calculates, The stress measuring device as described in any one of Claim 1 thru | or 5 characterized by the above-mentioned. In the first region of the glass containing lithium ions from the surface to the ion concentration transition point in the depth direction, lithium ions are replaced with potassium ions, and in the second region below the ion concentration transition point, lithium ions are replaced with sodium ions. A method for measuring stress of chemically strengthened glass, comprising:
In the chemically strengthened glass, a light supply step of making light from a light source incident,
Light propagating in the chemically strengthened glass, through a light extraction member, a light extraction step of emitting to the outside of the chemically strengthened glass,
Two or more bright lines, which are included in the light emitted to the outside of the chemically tempered glass and vibrate in parallel and perpendicularly to the boundary surface between the chemically tempered glass and the light extraction member, are provided. A light conversion step of converting into two types of emission line arrays having
An imaging step of imaging the two types of bright line arrays,
A position measuring step of measuring the positions of two or more bright lines in each of the two types of bright line arrays from the image obtained in the imaging step, and the position of the end point of the stress distribution in the first region;
A stress distribution calculating step of calculating the stress distribution of the first region based on the position of the bright line measured in the position measuring step and the position of the end point of the stress distribution of the first region;
The second region of the chemically strengthened glass to be measured based on the stress distribution of the first region calculated in the stress distribution calculation step and the stress distribution of the representative second region of the chemically strengthened glass measured in advance. A stress distribution estimation process for estimating the stress distribution of
A stress measurement comprising: combining the stress distribution of the first region and the stress distribution of the second region, and calculating a total stress distribution of the first region and the second region. Method. A stress measurement step of measuring a stress distribution in a typical second region of the chemically strengthened glass,
The stress measurement step,
A polarization phase difference changing step of changing the polarization phase difference of the laser light by one wavelength or more with respect to the wavelength of the laser light;
The scattered light emitted by the laser light having a variable polarization phase difference is incident on the chemically strengthened glass, multiple times at a predetermined time interval, an imaging step of acquiring a plurality of images,
Using the plurality of images to measure the periodic brightness change of the scattered light, calculate the phase change of the brightness change, the stress distribution in the depth direction from the surface of the chemically strengthened glass based on the phase change. 8. The stress measuring method according to claim 7, further comprising a calculation step of calculating.