A reflective glass edge stress meter

Abstract

This application discloses a reflective glass edge stress meter, comprising a housing, an illumination unit, and a detection unit. The housing has a detection opening defining the plane to be tested. During testing, the edge of the glass to be tested is along the x-direction within the plane, and the direction perpendicular to the edge is the y-direction within the plane. The illumination unit includes a light source and a polarizer, providing linearly polarized detection light that passes through the detection opening and illuminates the edge of the glass to be tested. The detection unit includes a light wedge and an analyzer. The illumination unit and the detection unit are positioned on the same side of the plane to be tested. The detection unit receives reflected light from the glass and forms interference fringes. The optical axis of the illumination unit is inclined relative to the plane to be tested, and the optical axis of the detection unit is substantially perpendicular to the plane to be tested. Embodiments of this invention can advantageously improve the accuracy of stress detection.

Description

Technical Field

[0001] This utility model relates to a technology for detecting glass stress using optical means, specifically, to a reflective glass edge stress meter. Background Technology

[0002] Glass is a common material in daily life and industrial production. During the forming and subsequent processing of glass, stress is generated due to bending, uneven cooling, and other factors. Compressive stress typically occurs at the edges, while tensile stress occurs near the edges. As tensile stress increases, the glass strength decreases, and the risk of spontaneous breakage increases. Therefore, it is necessary to monitor and control the stress at the glass edges to improve strength and reduce the risk of spontaneous breakage. Since stress causes birefringence in glass, the stress state at the glass edges can be calculated by measuring the optical path difference produced when polarized light passes through the glass.

[0003] When measuring edge stress in glass, light typically needs to pass through the glass, from one surface to the other, to detect birefringence caused by the stress. However, some glasses have a light-blocking layer (completely blocking or partially transmitting light), such as an ink layer, on one surface, preventing light from penetrating. Therefore, a reflective detection optical path has been proposed. For example, if surface a of the glass is coated with an ink layer while surface b is not, polarized light can be used to illuminate the glass from surface b. The light passes through the glass layer, illuminates surface a, is reflected, passes through the glass layer again, and exits from surface b. Finally, the stress in the glass is measured by detecting the optical path difference in the outgoing light. The reflective detection optical path effectively solves the problem of measuring glass stress using the birefringence effect when a light-blocking layer is present on the glass surface. However, the accuracy of glass stress detection based on the reflective detection optical path and the optimization of the device structure still need further improvement. Utility Model Content

[0004] The purpose of this invention is to provide a reflective glass edge stress meter that can at least partially overcome the shortcomings of the prior art.

[0005] According to one aspect of the present invention, a reflective glass edge stress meter based on optical wedge compensation is provided, comprising a housing and an illumination unit and a detection unit disposed within the housing, wherein:

[0006] The housing is provided with a detection opening, which defines a plane to be detected. When the glass to be detected is positioned at the detection opening, the edge of the glass to be detected is along the x-direction within the plane to be detected, and the direction perpendicular to the edge of the glass to be detected is the y-direction within the plane to be detected.

[0007] The illumination unit includes a light source and a polarizer for providing linearly polarized detection light, which passes through the detection opening and illuminates the edge of the glass to be tested.

[0008] The detection unit includes an optical wedge and an analyzer. Light from the glass to be tested passes sequentially through the optical wedge and the analyzer, forming interference fringes.

[0009] The illumination unit and the detection unit are disposed on the same side of the plane to be tested, such that the detection unit receives the reflected light of the linearly polarized detection light on the glass to be tested, wherein the optical axis of the illumination unit is inclined relative to the plane to be tested, and the optical axis of the detection unit is substantially perpendicular to the plane to be tested.

[0010] Preferably, the optical axis of the illumination unit forms a predetermined angle α with respect to the normal of the plane to be detected, 30°<α<55°, more preferably 40°≤α≤50°, and more preferably α=45°±2°.

[0011] Preferably, the reflective glass edge stress meter includes only a single illumination unit, which is arranged asymmetrically with respect to the optical axis of the detection unit.

[0012] Preferably, the linearly polarized detection light illuminating the glass to be tested has an angle relative to the optical axis of the illumination unit.

[0013] Preferably, the linearly polarized detection light is parallel to the x-direction relative to the incident surface of the plane to be detected.

[0014] Preferably, the polarization direction of the polarizer forms an angle φ1 with respect to the incident surface, where 40°≤φ1≤50°.

[0015] Preferably, the optical wedge is configured such that the phase difference it introduces varies along the x-direction and remains constant along the y-direction, and the polarization direction of the analyzer forms an angle φ2 with the x-direction, where φ2 = φ1.

[0016] Preferably, the reflective glass edge stress meter further includes an observation device disposed downstream of the detection unit. The observation device includes a camera for acquiring an image of the interference fringes formed by the detection unit. The camera is used to acquire the image with a field of view (FOV) ≤ 12°, preferably FOV ≤ 10°, and more preferably FOV ≤ 8°.

[0017] Preferably, the housing includes a first housing, a second housing, and a third housing. The bottom of the first housing is provided with the detection opening. The second housing and the third housing are connected to the upper part of the first housing, respectively accommodating the light source and the observation device, and separating the optical path upstream of the polarizer from the optical path downstream of the analyzer.

[0018] Preferably, the reflective glass edge stress meter further includes an optical path folding unit disposed between the detection unit and the observation device. The optical path folding unit includes a right-angle prism or two reflectors arranged at right angles to each other, for folding the optical path downstream of the detection unit by 180°.

[0019] In the reflective glass edge stress meter according to an embodiment of this utility model, the optical axis of the illumination unit is inclined relative to the plane to be tested, while the optical axis of the detection unit is substantially perpendicular to the plane to be tested. This allows the detection unit to receive the portion of the reflected light with the highest intensity and minimal change in intensity with angle from the Lambertian-distributed reflected light obtained from the light-shielding layer of the glass to be tested. This improves the brightness uniformity of the interference fringe image generated by the detection unit, thereby enhancing the accuracy of stress detection.

[0020] Furthermore, according to a preferred embodiment of the present invention, by selecting the range of angles formed by the optical axis of the illumination unit relative to the normal of the plane to be detected, selecting the angle of polarization detection light, and / or selecting the field of view range when the camera acquires the interference fringe image, it is advantageous to avoid the portion of the reflected light with drastic changes in intensity with angle in the Gaussian distributed reflected light reflected by the light-shielding layer of the glass to be detected from entering the detection unit and observation device, thereby further improving the brightness uniformity and contrast of the interference fringe image and thus improving the detection accuracy. Attached Figure Description

[0021] Other features, objects, and advantages of this invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0022] Figure 1 A perspective view of an example of a reflective glass edge stress meter according to an embodiment of the present invention;

[0023] Figure 2 for Figure 1 A schematic perspective view of the reflective glass edge stress meter shown.

[0024] Figure 3 for Figure 1 The front view of the reflective glass edge stress meter shown.

[0025] Figure 4 for Figure 1 The side view of the reflective glass edge stress meter shown;

[0026] Figure 5 This is a schematic optical path diagram of a reflective glass edge stress meter according to an embodiment of the present invention;

[0027] Figure 6 This is a schematic diagram showing the change in light intensity as a function of angle for reflected light from the scattering surface of an object under the Lambert and Gaussian models.

[0028] Figure 7 The interference fringe images obtained when the optical axis of the illumination unit forms an angle of 25° and 45° with respect to the normal of the glass surface to be tested are shown;

[0029] Figure 8 The schematic diagram illustrates the distribution of the incident angle of the detection light with a predetermined angle relative to the plane to be detected;

[0030] Figure 9 The schematic diagram illustrates the angle between the reflected light received by a camera with a predetermined FOV and the direction of specular reflection.

[0031] Figure 10 An exemplary diagram illustrating how the polarization direction of the polarizer and analyzer is set.

[0032] Figure 11 , Figure 12 and Figure 13 Examples of first, second, and third interference fringe images detected by a reflective glass edge stress meter according to an embodiment of the present invention are shown respectively.

[0033] Figure 14 An example of a glass edge stress curve obtained using a reflective glass edge stress meter according to an embodiment of the present invention is shown;

[0034] Figure 15 A schematic diagram for detecting the propagation path and polarization state of light in a glass sample. Detailed Implementation

[0035] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention. For ease of description, only the parts relevant to the invention are shown in the accompanying drawings.

[0036] It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other.

[0037] Figures 1 to 4 An example of a reflective glass edge stress meter according to an embodiment of the present invention is shown in different views, wherein Figure 1 It is a 3D image. Figure 2 This is a schematic structural perspective view. Figure 3 and Figure 4 The front view and right view are shown respectively. Figure 5 A schematic optical path diagram of a reflective glass edge stress meter according to an embodiment of the present invention is shown.

[0038] According to an embodiment of the present invention, a reflective glass edge stress meter 1 includes a housing 10 (see...). Figure 1 ) and the lighting unit 20 and the detection unit 30 disposed within the housing 10 (see Figure 2 and Figure 5 ).

[0039] See Figure 4 The housing 10 is provided with a detection opening 10a, which defines the plane to be detected (i.e., the xy plane). When the glass G to be detected is positioned at the detection opening 10a, the edge of the glass G is along the x-direction within the plane to be detected, and the direction perpendicular to the edge of the glass G is the y-direction within the plane to be detected. Preferably, as shown... Figure 1 and Figure 4 As shown, a positioning block 10b is provided on one side of the detection opening 10a for the edge of the glass G to be tested to abut against, so as to more conveniently and reliably position the edge parallel to the x-direction. Optionally, as shown... Figures 1 to 4 As shown, the housing 10 also includes a base plate 10c, which can serve as part of the detection opening 10a, defining the plane to be detected (i.e., the xy plane).

[0040] The illumination unit 20 includes a light source 21 and a polarizer 22. The polarizer 22 receives light from the light source 21 and converts it into linearly polarized detection light PL (see [link to relevant documentation]). Figure 5 The light source 21 can be a white light source, such as a white LED. Alternatively, the light source 21 may include an array of light-emitting devices, such as an LED array. To improve light utilization efficiency, a condenser lens 23 may be optionally placed between the light source 21 and the polarizer 22 to focus the light onto a predetermined area of ​​the polarizer. The linearly polarized detection light provided by the illumination unit 20 passes through the detection opening 10a and illuminates the edge of the glass G to be tested.

[0041] Advantageously, such as Figures 1 to 3 As shown, the reflective glass edge stress meter 1 may include only a single illumination unit 20, which is arranged asymmetrically with respect to the optical axis O2 of the detection unit 30.

[0042] Linearly polarized detection light can be considered as having a first polarization direction perpendicular to the plane of incidence (see...). Figure 10 p as shown 11The first polarized light and the second polarized light having a direction parallel to the plane of incidence (see...) Figure 10 p as shown 12 It is formed by the superposition of the second polarized light. For example... Figure 4 The polarized light illuminating the upper surface of the glass G under test is reflected by the light-shielding layer Ga on the lower surface and returns to the upper surface, then is transmitted back through the glass G. During this process, the birefringence effect caused by stress at the edge of the glass G results in an optical path difference between the first and second polarized light.

[0043] According to an embodiment of the present invention, a reflective glass edge stress meter employs an optical wedge compensation method to detect the optical path difference caused by the birefringence effect of the glass, thereby measuring the stress at the glass edge. For this purpose, the detection unit 30 of the reflective glass edge stress meter 1 includes an optical wedge 31 and an analyzer 32, such that light from the glass G to be tested passes sequentially through the optical wedge 31 and the analyzer 32, forming interference fringes. The illumination unit 20 and the detection unit 30 are disposed on the same side of the plane to be tested, such that the detection unit 30 receives the reflected light from the linearly polarized detection light on the glass G to be tested. Preferably, the optical wedge 31 is configured such that the phase difference it introduces varies along the x-direction and remains constant along the y-direction. The optical wedge 31 can be, for example, a quartz wedge or any other optical element capable of generating the desired optical path difference. Figure 2 In the example shown, the analyzer 32 is formed as a polarizing film on the surface of the optical wedge 31. In other examples, the analyzer 32 may also be formed as a separate element from the optical wedge 31.

[0044] According to an embodiment of the present invention, the illumination unit 20 and the detection unit 30 are arranged such that the optical axis O1 of the illumination unit 20 is inclined relative to the plane to be detected (the angle between the optical axis O1 and the normal to the plane to be detected is greater than 0° and less than 90°), while the optical axis O2 of the detection unit 30 is substantially perpendicular to the plane to be detected. Figure 2 and Figure 5 As shown. This allows the detection unit 30 to receive the portion of ideal diffuse reflection light with maximum intensity under the Lambertian model, reflected from the light-shielding layer Ga of the glass G to be tested, while avoiding the strong reflection light in and around the specular reflection direction. This helps improve the brightness uniformity and contrast of the interference fringe image generated by the detection unit 30, thereby improving the stress detection accuracy.

[0045] Specifically, the surface light-shielding layer (e.g., ink layer) of glass requiring stress testing (such as a vehicle windshield) is typically a non-specular reflective layer. This means that such a light-shielding layer will produce scattering. Different reflective layer surface characteristics result in different scattering characteristics. Existing scattering analysis models include the Lambert model and the Gaussian model.

[0046] An ideal diffuse reflective surface is called a Lambertian surface. The Lambertian model refers to the fact that the intensity of reflected light from a Lambertian surface is not affected by the incident angle of the light, and has a spatial distribution characteristic that conforms to the cosine law, such as... Figure 6 As shown in figure (a). Specifically, the intensity of diffuse reflected light from the Lambertian surface at different angles varies according to the cosine of the angle between the ray and the surface normal, i.e., it satisfies:

[0047] P = P0cosθ

[0048] Where P0 is the intensity of the reflected light along the surface normal direction, which is also the maximum intensity, and P and θ are the intensity of the reflected light and the angle with the surface normal, respectively.

[0049] The Gaussian model refers to the Gaussian distribution of light intensity reflected from an object's surface, such as... Figure 6 As shown in figure (b), the light intensity satisfies:

[0050]

[0051] Where P'0 is the intensity of the reflected light along the specular reflection direction of the incident light, which is also the maximum intensity, and P' and θ' are the intensity of the reflected light and the angle with the specular reflection direction, respectively.

[0052] Considering that the reflection of the light-shielding layer Ga on the surface of the glass to be tested is difficult to simulate and analyze simply using the Lambert model or the Gaussian model, the inventors of this utility model assume that the reflection of the light-shielding layer Ga is a superposition of two scattering methods that conform to the Lambert model and the Gaussian model, respectively. Furthermore, in the reflective glass edge stress meter according to the embodiment of this utility model, the optical axis O1 of the illumination unit 20 is set to be inclined relative to the plane to be tested, while the optical axis O2 of the detection unit 30 is set to be substantially perpendicular to the plane to be tested. Under the aforementioned assumptions and settings, the scattering of the detection light provided by the illumination unit 20 on the shielding layer Ga produces both the reflected light with maximum intensity P0 along the surface normal direction n under the Lambertian model and the reflected light with maximum intensity P'0 along the specular reflection direction m under the Gaussian model. The detection unit 30 avoids the reflected light with maximum intensity P'0 along the specular reflection direction m under the Gaussian model and the reflected light with strong intensity in its vicinity, while receiving and detecting the reflected light with maximum intensity P0 along the surface normal direction n under the Lambertian model and the reflected light in its vicinity whose intensity does not change significantly with the reflection angle. This is beneficial for improving the brightness uniformity of the interference fringe image.

[0053] Furthermore, the asymmetrical arrangement of the optical axes of the illumination unit 20 and the detection unit 30 relative to the normal n of the glass surface allows the detection unit 30 to avoid specular reflection of the detection light on the upper surface of the glass G to be tested (the surface opposite to the surface on which the light-shielding layer is formed), which helps to improve the contrast of the interference fringes and thus improve the detection accuracy.

[0054] According to advantageous embodiments of the present invention, such as Figure 5 As shown, the optical axis O1 of the illumination unit 20 forms a predetermined angle α with respect to the normal n of the plane to be detected, where 30° < α < 55°. Here, by selecting an angle α greater than 30°, the specular reflection direction can be made more deviated from the normal n, thereby reducing the portion of reflected light whose intensity decreases sharply as the reflection direction approaches the normal in the aforementioned Gaussian model from entering the detection unit 30, which is beneficial for improving the brightness uniformity of the interference fringe image. At the same time, by selecting an angle α less than 55°, the linearly polarized detection light from the illumination unit 20 can be more focused onto the area to be detected, improving the illumination brightness. Preferably, 40° ≤ α ≤ 50°, more preferably α = 45° ± 2°, to better improve the brightness uniformity of the interference fringe image and improve illumination, thereby improving detection accuracy.

[0055] For example only, Figure 7 Figures (a) and (b) show interference fringe images obtained at angles α = 25° and α = 45° relative to the normal of the glass surface under test, respectively. Comparing figures (a) and (b), it can be seen that when α = 25°, the brightness of the interference fringe image is significantly uneven, especially at the upper part of the image where whitening occurs due to brightness saturation, resulting in incomplete fringe display. In contrast, when α = 45°, the brightness of the interference fringe image is more uniform, and the fringe display is more complete, which is beneficial for more accurate identification of the order and position of the interference fringes, thereby enabling more accurate calculation of optical path difference and stress.

[0056] Return to reference Figure 2 and Figure 5 The reflective glass edge stress meter 1 may also include an observation device 40 disposed downstream of the detection unit 30. The observation device 40 includes a camera 41 for acquiring images of the interference fringes formed by the detection unit 30. In this way, in addition to visually observing the interference fringes, automatic stress detection and analysis can be achieved by acquiring electronic images of the interference fringes and performing image processing on the electronic images.

[0057] In addition, such as Figure 2 As shown, the reflective glass edge stress meter 1 may further include an optical path folding unit 50 disposed between the detection unit 30 and the observation device 40, for folding the optical path downstream of the detection unit 30 by 180°. Figure 2In the example shown, the optical path folding unit 50 includes two mirrors arranged at right angles to each other; in other examples, the optical path folding unit 50 may include, for example, a right-angle prism.

[0058] Preferably, such as Figure 5 As shown, the linearly polarized detection light PL illuminating the glass G to be tested has an angle relative to the optical axis O1 of the illumination unit 20. and By opening the angle By limiting the incident angle of the detection light on the glass under test to a certain range, it is possible to prevent some reflected light with drastic changes in light intensity under the Gaussian model from entering the detection unit 30 when the incident angle is too small. Simultaneously, it helps to prevent the light energy of the detection light on the glass under test from being too dispersed, resulting in insufficient or uneven illumination, when the incident angle is too large. For ease of understanding, Figure 8 The schematic diagram illustrates the angle subtended by the optical axis O1 relative to the illumination unit 20. The incident angle distribution of the detection light relative to the plane to be detected is shown in Figure (a), where the angle α between the optical axis O1 and the normal n of the plane to be detected is 45°, and the angle α between the optical axis O1 and the normal n of the plane to be detected is 30°.

[0059] like Figure 5 As shown, the field of view (FOV) of camera 41 for acquiring the interference fringe image is 12°. Preferably, FOV ≤ 12°. By limiting the FOV to the above-mentioned small angle range, the reflection angle of the reflected light received by camera 41 can be limited to a small range, which helps to reduce the amplitude of the change in reflected light intensity with the angle, thereby improving the brightness uniformity of the image. Figure 9 The schematic diagram illustrates the angle between the reflected light received by a camera with a predetermined field of view and the direction of reflection from the specular surface. In the case shown in Figure (a), the angle α between the optical axis O1 and the normal n of the plane to be detected is 45°, and the angle subtended by the detection light relative to the optical axis O1 is... Furthermore, FOV≈8°; in the case shown in Figure (b), the angle α between the optical axis O1 and the normal n of the plane to be detected is 30°, and the angle subtended by the detection light relative to the optical axis O1 is... And the field of view (FOV) is approximately 10°.

[0060] According to the preferred embodiment of this utility model, such as Figure 5 As shown, the linearly polarized detection light is parallel to the x-direction relative to the incident surface of the plane to be detected, that is, parallel to the extension direction of the edge of the glass G to be detected.

[0061] Figure 10 A diagram illustrating a preferred example of how the polarization directions of the polarizer 22 and analyzer 32 are set. (e.g.) Figure 10As shown, the polarization direction p1 of the polarizer 22 forms an angle φ1 with respect to the incident surface (i.e., the plane containing the optical axis O1 and the surface normal (same as the z-axis) of the glass G to be tested), preferably 40°≤φ1≤50°. Furthermore, the optical wedge 31 is configured such that the phase difference it introduces varies along the x-direction and remains constant along the y-direction, and as... Figure 10 As shown, the polarization direction p2 of the analyzer 32 forms an angle φ2 with the x-direction, where φ2 = φ1.

[0062] Return to continue referencing Figure 2 and Figure 5 According to a preferred embodiment of the present invention, the observation device 40 further includes a calculation unit 42. The calculation unit 42 calculates the stress at the edge of the glass G to be detected based on the image, wherein the calculation unit 42 is configured to perform the following processing:

[0063] (1) Obtain the first interference fringe image with a diffuse reflector placed at the detection opening, and record the x-direction position P0 of each fringe corresponding to a y-direction position Py, wherein the diffuse reflector does not introduce optical path difference.

[0064] (2) Obtain the second interference fringe image with a diffuse reflector placed at the detection opening and a standard sheet superimposed on the diffuse reflector, and record the x-direction position P1 of each fringe corresponding to the y-direction position, where the total optical path difference introduced by the standard sheet is OPDA.

[0065] (3) Obtain the third interference fringe image when the glass to be tested is placed at the detection opening, and record the x-direction position PX of each fringe corresponding to the y-direction position;

[0066] (4) Calculate the total optical path difference introduced by the glass G to be tested.

[0067] For ease of understanding, Figure 11 , Figure 12 and Figure 13 Examples of the first interference fringe image, the second interference fringe image, and the third interference fringe image detected by the reflective glass edge stress meter 1 according to an embodiment of the present invention are shown respectively.

[0068] As an example, Figure 14 The diagram shows a glass edge stress curve obtained using a reflective glass edge stress meter according to an embodiment of the present invention, where the horizontal axis represents the distance / length from the edge of the glass to be tested, and the vertical axis represents the stress value, where negative values ​​represent compressive stress and positive values ​​represent tensile stress.

[0069] According to a preferred embodiment of the present invention, the calculation unit 42 uses the total optical path difference (OPDA) determined according to the following formula:

[0070]

[0071] Wherein, α is the predetermined angle formed by the optical axis O1 of the illumination unit 20 with respect to the normal of the plane to be detected; To detect the angle of refraction after light shines on a standard sample; R is the refractive index of the standard sample; t is the thickness of the standard sample; σ x ρ represents the stress in the x-direction of the standard sheet (the stress direction is parallel to the x-direction); PE is the photoelastic coefficient of the standard sheet.

[0072] A standard piece refers to a piece with known t*σ. x * Glass slide with PE value.

[0073] The above formula is based on the following accurate calculations of stress and propagation path length, which take into account the influence of the propagation direction of the light refracted into the standard plate on stress and propagation path length.

[0074] (Direction of dissemination)

[0075] like Figure 15 As shown, linearly polarized detection light (PL) illuminates one surface of a glass sample (e.g., a standard sheet) and enters the glass through refraction. The refracted light lies within the incident plane (i.e., the xz plane), and the refraction angle is... (Air has a refractive index of 1, glass has a refractive index of R, and the angle of incidence is α); after the refracted light is reflected on the other surface of the glass plate, the reflected light with a reflection angle of 0° exits from the glass plate.

[0076] (Propagation path length)

[0077] The length L of the propagation path of light within the glass plate is the sum of the first length L1 of the refracted light propagating along the direction determined by the refraction angle β and the second length L2 of the reflected light propagating along the perpendicular path, i.e., L = L1 + L2 = t / cosβ + t, where t is the thickness of the glass plate.

[0078] (Stress decomposition)

[0079] In glass edge stress testing, the film stress of the glass sample is measured. The total optical path difference (OPDA) calculation formula mentioned above is based on the following film stress analysis model: the sample is simplified as a two-dimensional object in a plane xy, its thickness in the z direction is ignored, and the stress of the sample in the z direction is also ignored, i.e., σ z =0; there is no compressive or tensile stress at the edge of the sample in the y-direction perpendicular to the edge, i.e., σ y =0; the sample only has compressive or tensile stress in the x-direction parallel to the edge, i.e., σ x ! = 0; Stress σ in the x direction x The stress changes and reverses as the position of the detected part changes in the y-direction, thus forming a stress balance.

[0080] The polarization direction of light inside the glass is decomposed into two directions: one is the s-polarization direction, which is perpendicular to the incident plane (i.e., parallel to the y-direction), and the other is the p-polarization direction, which is in the incident plane and perpendicular to the direction of light propagation.

[0081] Light inside glass can be considered as a superposition of s-polarized and p-polarized light. The stress in the polarization direction of s-polarized light is zero (σ). y =0). In the path of the refracted light propagating along the direction determined by the refraction angle β, the stress σ in the polarization direction of the p-polarized light. a Not zero:

[0082]

[0083] (Optical path difference calculation)

[0084] The optical path difference (OPDI) introduced during the propagation of refracted light is:

[0085]

[0086] The optical path difference (OPDR) introduced during the propagation of reflected light within the glass slide is:

[0087] OPDR = L2 * σ x *PE=t*σ x *PE

[0088] The total optical path difference (OPDA) is:

[0089]

[0090] Taking an incident angle α = 45° and a glass refractive index of 1.52 as an example, the internal propagation angle of light in the glass sample is 28 degrees. After the light shines on the ink on the bottom surface, diffuse reflection occurs, and the reflected light with a reflection angle of 0° exits from inside the sample. Thus, the total optical path difference OPDA generated after the light passes through the sample is approximately 1.883OPDR.

[0091] Existing reflective glass edge stress testing devices typically use twice the optical path difference (i.e., 2OPDR) as the corresponding total optical path difference when light is incident perpendicularly on the standard plate and / or the glass under test. In contrast, the method described above for determining / calculating the total optical path difference (OPDR) in the reflective glass edge stress meter according to the present invention can effectively improve the accuracy of the finally obtained stress.

[0092] Furthermore, according to the preferred embodiment of this utility model, such as Figure 1 and Figure 2As shown more clearly in the diagram, the optical path arrangement corresponds to the illumination unit's optical axis being inclined relative to the plane to be detected, while the detection unit's optical axis is substantially perpendicular to the plane to be detected. The housing 10 may include a first housing 11, a second housing 12, and a third housing 13. A detection opening 10a is provided at the bottom of the first housing 11. The second housing 12 and the third housing 13 are connected to the upper part of the first housing 11, respectively accommodating the light source 21 and the observation device 40, and separating the optical path upstream of the polarizer 22 from the optical path downstream of the analyzer 32. Preferably, an aperture can be provided around the polarizer 22 and / or around the optical wedge and / or the analyzer 32 to reduce stray light in the detection space and improve the signal-to-noise ratio of the interference fringe image.

[0093] In addition, such as Figure 1 As shown more clearly in the diagram, a handle 10d may be provided on the side of the first housing 11 opposite to the second housing 12 to facilitate the holding and carrying of the stress meter.

[0094] The above description is merely a preferred embodiment of this application and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of the invention involved in this application is not limited to technical solutions formed by specific combinations of the above-described technical features, but should also cover other technical solutions formed by arbitrary combinations of the above-described technical features or their equivalents without departing from the inventive concept. For example, technical solutions formed by substituting the above features with (but not limited to) technical features with similar functions disclosed in this application.

Claims

1. A reflective glass edge stress meter based on optical wedge compensation, comprising a housing and an illumination unit and a detection unit disposed within the housing, characterized in that: The housing is provided with a detection opening, which defines a plane to be detected. When the glass to be detected is positioned at the detection opening, the edge of the glass to be detected is along the x-direction within the plane to be detected, and the direction perpendicular to the edge of the glass to be detected is the y-direction within the plane to be detected. The illumination unit includes a light source and a polarizer for providing linearly polarized detection light, which passes through the detection opening and illuminates the edge of the glass to be tested. The detection unit includes an optical wedge and an analyzer. Light from the glass to be tested passes sequentially through the optical wedge and the analyzer, forming interference fringes. The illumination unit and the detection unit are disposed on the same side of the plane to be tested, such that the detection unit receives the reflected light of the linearly polarized detection light on the glass to be tested, wherein the optical axis of the illumination unit is inclined relative to the plane to be tested, and the optical axis of the detection unit is perpendicular to the plane to be tested.

2. The reflective glass edge stress meter of claim 1, wherein, The optical axis of the illumination unit forms a predetermined angle a, 30 with respect to the normal of the plane to be detected o <α<55 o .

3. The reflective glass edge stress meter of claim 2, wherein the light source is a laser diode. 5 40 o ≤α≤50 o 。 4. The reflective glass edge stress meter of claim 3, wherein, α=45 o ±2 o 。 5. The reflective glass edge stress meter of claim 2, wherein, The reflective glass edge stress meter includes only a single illumination unit, which is arranged asymmetrically with respect to the optical axis of the detection unit.

6. The reflective glass edge stress meter of claim 1, wherein, The linearly polarized detection light irradiated onto the glass to be detected has an opening angle φ with respect to the optical axis of the illumination unit, φ ≤ 6 o .

7. The reflective glass edge stress meter according to any one of claims 1 to 6, wherein The linearly polarized detection light is parallel to the x-direction relative to the incident surface of the plane to be detected.

8. The reflective glass edge stress meter of claim 7, wherein, The polarizing direction of the polarizer forms an angle Φ1 with the incident plane, 40 o ≤ Φ1 ≤ 50 o .

9. The reflective glass edge stress meter of claim 8, wherein, The optical wedge is configured such that the phase difference it introduces varies along the x-direction and remains constant along the y-direction, and the polarization direction of the analyzer forms an angle Φ2 with the x-direction, where Φ2 = Φ1.

10. The reflective glass edge stress meter of any one of claims 1-6, wherein, Also included is an observation device disposed downstream of the detection unit, the observation device comprising a camera for acquiring an image of the interference fringes formed by the detection unit, the camera being configured to acquire the image with a field of view FOV≤12° o .

11. The reflective glass edge stress meter of claim 10, wherein, the field of view FOV < 10 o .

12. The reflective glass edge stress meter of claim 11, wherein, the field of view FOV < 8 o .

13. The reflective glass edge stress meter of claim 10, wherein, The housing includes a first housing, a second housing, and a third housing. The bottom of the first housing is provided with the detection opening. The second housing and the third housing are connected to the upper part of the first housing, respectively accommodating the light source and the observation device, and separating the optical path upstream of the polarizer from the optical path downstream of the analyzer.

14. The reflective glass edge stress meter of claim 10, wherein, The application further comprises a light path folding unit arranged between the detection unit and the observation device, the light path folding unit comprising a right-angle prism or two mirrors arranged at right angles to each other, for folding the light path downstream of the detection unit by 180 o .

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