Mirror surface shape measurement device, mirror surface shape measurement method, and plate glass manufacturing method

Abstract

Provided is a technique for improving measurement accuracy of a shape of a mirror surface of an object to be measured. This mirror surface shape measurement device measures a shape of a mirror surface of an object to be measured that specularly reflects a light beam of a prescribed wavelength. This mirror surface shape measurement device is provided with a distance measurement device and a reflection pattern. The distance measurement device has a light source, a plurality of light receiving elements, and a control circuit. The control circuit measures the time of flight (ToF) of the light beam from the light source through the mirror surface, the reflection pattern, and the mirror surface in this order to reach each of the light receiving elements, creates an image showing the coordinates of the reflection pattern reflected on the mirror surface, identifies the coordinates of the turning points of the light beam in the reflection pattern, and identifies the coordinates of the reflection points for each path of the light beam received by each of the light receiving elements.

Description

Mirror surface shape measuring device, mirror surface shape measuring method, and plate glass manufacturing method

[0001] The present disclosure relates to a mirror surface shape measuring device, a mirror surface shape measuring method, and a glass sheet manufacturing method.

[0002] The shape measuring device described in Patent Document 1 captures images of the pattern reflected on the surface of the glass plate before and after the glass plate is moved, and measures the shape of the surface of the glass plate based on the two images and the distance the glass plate is moved.

[0003] The distance measuring device described in Patent Document 2 measures the time of flight (ToF) of light irradiated toward an object to be measured, which is reflected by the object and returns to the distance measuring device. The object diffusely reflects the light, causing the light to return to the distance measuring device.

[0004] Patent No. 5817721 International Publication No. 2022 / 107512

[0005] The shape measuring device disclosed in Patent Document 1 moves a glass plate to acquire two images. Since the movement distance of the glass plate is used to measure the shape of the mirror surface, errors in the movement distance and the like reduce the measurement accuracy of the shape of the mirror surface.

[0006] The distance measuring device in Patent Document 2 measures the time of flight of light irradiated toward an object to be measured, which is diffusely reflected by the object and returns. If the reflective surface of the object to be measured is a mirror, the light is reflected by the mirror and does not return to the distance measuring device. Therefore, the shape of the mirror surface cannot be measured.

[0007] Conventional ToF distance measuring devices cannot measure the shape of the mirror surface of a measurement target. Therefore, there are technical obstacles to combining the shape measuring device of Patent Document 1 with the distance measuring device of Patent Document 2.

[0008] One embodiment of the present disclosure provides a technique for improving the measurement accuracy of the shape of a mirror surface of a measurement object.

[0009] A mirror surface shape measuring device according to one embodiment of the present disclosure measures the shape of a mirror surface of a measurement target that specularly reflects light rays of a predetermined wavelength. The mirror surface shape measuring device includes a distance measuring device and a reflection pattern. The distance measuring device includes a light source that irradiates the light rays toward multiple reflection points on the mirror surface, multiple light receiving elements that receive the light rays returning from the multiple reflection points, and a control circuit that controls the light source and creates an image according to the light receiving intensity of each of the light receiving elements. The reflection pattern is disposed at a distance from the mirror surface and diffusely reflects the light rays specularly reflected from the multiple reflection points toward the multiple reflection points. The control circuit measures the time of flight (ToF) of the light ray from the light source through the mirror surface, the reflection pattern, and the mirror surface in this order to reach each of the light receiving elements, creates an image showing the coordinates of the reflection pattern reflected on the mirror surface, identifies the coordinates of the turning points of the light ray in the reflection pattern, and identifies the coordinates of the reflection points for each path of the light ray received by each of the light receiving elements.

[0010] According to an embodiment of the present disclosure, it is possible to improve the measurement accuracy of the shape of the mirror surface of the measurement object.

[0011] Fig. 1 is a perspective view showing a mirror surface shape measuring device according to one embodiment. Fig. 2 is a cross-sectional view showing an example of a path of a light ray received by one light receiving element. Fig. 3 is a cross-sectional view showing an example of a path of a light ray received by another light receiving element. Fig. 4 is a flowchart showing a glass sheet manufacturing method according to one embodiment.

[0012] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In each drawing, the same or similar components are denoted by the same reference numerals, and their description may be omitted. In the specification, the symbol "to" indicating a numerical range means that the numerical values ​​before and after it are included as the lower and upper limits. The numerical range includes the range rounded up or down.

[0013] 1 to 3, a mirror surface shape measuring device 1 and a mirror surface shape measuring method according to one embodiment will be described. The mirror surface shape measuring device 1 measures the shape of a mirror surface 2a of a measurement object 2 that specularly reflects a light beam LB of a predetermined wavelength. The measurement object 2 is, for example, a glass plate. The glass plate is bent in advance. The mirror surface 2a may be a curved surface.

[0014] The mirror surface 2a preferably has an arithmetic mean roughness Ra of 0.0 μm or more and less than 0.2 μm. The arithmetic mean roughness Ra is measured in accordance with JIS B0031:2013. If the arithmetic mean roughness Ra of the mirror surface 2a is less than 0.2 μm, the light ray LB is almost entirely specularly reflected by the mirror surface 2a. The light ray LB is almost not diffusely reflected by the mirror surface 2a.

[0015] The mirror surface shape measuring device 1 includes a distance measuring device 10. The distance measuring device 10 includes, for example, a ToF (Time of Flight) camera. The distance measuring device 10 measures the shape of the mirror surface 2 a by measuring the time of flight (ToF) of a light beam LB traveling from the light source 11 through the mirror surface 2 a, the reflection pattern 20, and the mirror surface 2 a in this order to reach each light receiving element 12.

[0016] The distance measuring device 10 has a light source 11, multiple light receiving elements 12, and a control circuit 13. The light source 11 emits light beams LB toward multiple reflection points P1 (see FIGS. 2 and 3) on the mirror surface 2a. The multiple light receiving elements 12 receive the light beams LB returning from the multiple reflection points P1. The control circuit 13 controls the light source 11 and creates an image according to the light receiving intensity of each light receiving element 12.

[0017] The light source 11 emits light beams LB toward a plurality of reflection points P1 on the mirror surface 2a. Although there are no particular limitations on the light beams LB, they are preferably near-infrared light with a wavelength of approximately 850 nm to 940 nm. The light source 11 includes, for example, a semiconductor laser or an LED. The light source 11 emits the light beams LB at a desired timing under the control of the control circuit 13. The light beams LB are diffused by a diffusion lens (not shown) or the like and are incident on the plurality of reflection points P1.

[0018] The plurality of light receiving elements 12 receive light beams LB returning from the plurality of reflection points P1. The light beams LB are focused by a focusing lens (not shown) or the like onto a light receiving surface on which the plurality of light receiving elements 12 are two-dimensionally arranged. Visible light such as sunlight becomes noise, so it is preferable to cut it using a visible light cut filter or the like before it is received by the light receiving elements 12. The plurality of light receiving elements 12 generate signals corresponding to the received light intensity of the light beams LB and transmit the signals to the control circuit 13.

[0019] The control circuit 13 is, for example, a computer. The control circuit 13 includes electronic circuits such as a CPU, a field programmable gate array (FPGA), or an application specific integrated circuit (ASIC), and performs various processes described in this specification by executing instruction codes stored in a memory or by being a circuit designed for a specific application. The processes of the control circuit 13 will be described later.

[0020] The mirror surface shape measuring device 1 includes a reflection pattern 20. The reflection pattern 20 is disposed at a distance from the mirror surface 2a. The reflection pattern 20 diffusely reflects a light beam LB that is specularly reflected at a plurality of reflection points P1 on the mirror surface 2a, back toward the original plurality of reflection points P1. The arithmetic mean roughness Ra of the reflection surface of the reflection pattern 20 is preferably 0.2 μm or more and 10 μm or less.

[0021] If the arithmetic mean roughness Ra of the reflecting surface of the reflecting pattern 20 is 0.2 μm or more, the reflecting pattern 20 diffusely reflects the light ray LB. In this way, even if the mirror surface 2a is curved, the light ray LB can be returned to the same reflection point P1 at the same angle. The outward path from the reflection point P1 to the turning point P2 coincides with the return path from the turning point P2 to the reflecting point P1.

[0022] The design of the reflection pattern 20 is not limited to the polka dots shown in Fig. 1, but may be a checkerboard pattern, etc. The pattern of the reflection pattern 20 may be any pattern that allows the coordinates of the turning point P2 (see Figs. 2 and 3) of the light ray LB in the reflection pattern 20 to be identified by image processing of an image showing the coordinates of the reflection pattern 20 reflected on the mirror surface 2a.

[0023] 2 and 3, an example of processing by the control circuit 13 will be described. The control circuit 13 measures the time of flight (ToF) of the light ray LB from the light source 11, passing through the mirror surface 2a, the reflection pattern 20, and the mirror surface 2a in this order, to reach each light receiving element 12. The time of flight is measured based on the irradiation timing of the light source 11 and the light reception timing of each light receiving element 12.

[0024] The path of the light ray LB received by each light receiving element 12 is different for each light receiving element 12. The path of the light ray LB received by each light receiving element 12 includes a different reflection point P1 for each light receiving element 12. The reflection point P1 exists on the optical axis 12L of the light receiving element 12, and the optical axis 12L of the light receiving element 12 is different for each light receiving element 12. It is sufficient that the reflection point P1 is different for each light receiving element 12, and the turning points P2 may overlap.

[0025] The control circuit 13 measures the total distance (L1+L2) of the distance L1 (not shown) from each light-receiving element 12 to each reflection point P1 and the distance L2 (not shown) from each reflection point P1 to each turning point P2, based on the time of flight of the light ray LB from the light source 11 through the reflection pattern 20 to each light-receiving element 12. The total distance (L1+L2) may be measured by either the direct ToF method or the indirect ToF method.

[0026] There can be many combinations of reflection point P1 and turning point P2 such that the total distance (L1 + L2) matches the measured value. However, reflection point P1 must exist on the optical axis 12L of the light receiving element 12. Therefore, if the coordinates of turning point P2 can be identified, the coordinates of reflection point P1 can also be identified.

[0027] The control circuit 13 creates an image showing the coordinates of the reflection pattern 20 reflected on the mirror surface 2a and identifies the coordinates of the turning point P2 of the light beam LB in the reflection pattern 20. The coordinates of the design of the reflection pattern 20 (for example, the center points of the polka dots or the intersection points of a grid) are stored in advance in a storage medium such as a memory, and are read out and used when identifying the coordinates of the turning point P2. The turning point P2 is, for example, the center point of the polka dots or the intersection points of a grid.

[0028] The control circuit 13 determines the coordinates of the reflection point P1 for each path of the light ray LB received by each light receiving element 12 based on the total distance (L1 + L2) and the coordinates of the turning point P2. By determining the coordinates of multiple reflection points P1 in this way, the shape of the mirror surface 2a can be measured. The control circuit 13 can also create a shape image showing the coordinates of each reflection point P1 (in other words, the shape of the mirror surface 2a) and display it on a display.

[0029] Hereinafter, to distinguish between different types of images, an image showing the distribution of the light receiving intensity of each light receiving element 12 will be referred to as a "received light intensity image," an image showing the coordinates of each reflection point P1 (in other words, the shape of the mirror surface 2a) will be referred to as a shape image, and an image showing the distribution of the time of flight will be referred to as a "time of flight image." All of these images can be displayed on a display. The brightness of the received light intensity image represents the distribution of the light receiving intensity, while the brightness of the shape image represents the shape of the mirror surface 2a (in other words, the distribution of the distance L1), and the brightness of the time of flight image represents the distribution of the time of flight.

[0030] The image used to identify the coordinates of the turning point P2 is a received light intensity image. The shape image cannot be created before identifying the coordinates of the turning point P2. The shape image is created after identifying the coordinates of the turning point P2 and the coordinates of the reflection point P1. This is because the distance L1 is unknown until the coordinates of the reflection point P1 are identified.

[0031] According to this embodiment, unlike the shape measuring device of Patent Document 1, it is not necessary to move the measurement object 2 to measure the shape of the mirror surface 2a. Therefore, it is not necessary to control the movement distance of the measurement object 2, and it is possible to prevent a decrease in the measurement accuracy of the shape of the mirror surface 2a due to an error in the movement distance, etc. Therefore, it is possible to improve the measurement accuracy of the shape of the mirror surface 2a.

[0032] The reflective pattern 20 is provided on a substrate 30. The substrate 30 may diffusely reflect the light LB, similar to the reflective pattern 20. The arithmetic mean roughness Ra of the reflective surface of the substrate 30 is preferably 0.2 μm or more and 10 μm or less. If the arithmetic mean roughness Ra of the reflective surface of the substrate 30 is 0.2 μm or more, the substrate 30 diffusely reflects the light LB.

[0033] When the substrate 30 diffusely reflects the light ray LB, it is preferable that the reflective surface of the substrate 30 and the reflective surface of the reflective pattern 20 have different arithmetic mean roughnesses Ra. In the received light intensity image, the contrast between the substrate 30 and the reflective pattern 20 can be ensured, and the outline of the pattern of the reflective pattern 20 can be identified.

[0034] When the substrate 30 diffusely reflects the light beam LB, the control circuit 13 preferably creates an image used to identify the coordinates of the turning point P2 based on the received light intensity of the second light beam. The second light beam is received by the light receiving element 12 separately from the light beam LB used to measure the time of flight. The received light intensity can be measured over a long exposure time. The second light beam and the light beam LB are formed at different times.

[0035] When the control circuit 13 creates an image used to identify the coordinates of the turning point P2 based on the received light intensity of the second light ray, it is preferable that the positions of the light source 11, the light receiving element 12, the measurement object 2, and the reflection pattern 20 are fixed when receiving the light ray LB and when receiving the second light ray. Since all positions are fixed, it is possible to prevent a decrease in the measurement accuracy of the reflection point P1 due to an error in the moving distance, etc.

[0036] Unlike the reflection pattern 20, the substrate 30 may specularly reflect the light ray LB. The arithmetic mean roughness Ra of the reflection surface of the substrate 30 is preferably 0.0 μm or more and less than 0.2 μm. The light ray LB specularly reflected by the substrate 30 is diffusely reflected by surrounding objects, and then specularly reflected again by the substrate 30 and returns to the reflection point P1. Therefore, there is a large difference in the time of flight between the substrate 30 and the reflection pattern 20, and the contrast between the substrate 30 and the reflection pattern 20 is sufficiently high in the time-of-flight image.

[0037] When the substrate 30 specularly reflects the light beam LB, the contrast between the substrate 30 and the reflection pattern 20 is sufficiently high in the time-of-flight image. Therefore, when the substrate 30 specularly reflects the light beam LB, it is preferable that the control circuit 13 create a time-of-flight image as an image to be used to identify the coordinates of the turning point P2. By measuring the time-of-flight and identifying the coordinates of the turning point P2 using the same light beam LB, the measurement accuracy of the reflection point P1 can be improved.

[0038] When the same light beam LB is used to measure the time of flight and to identify the coordinates of the turning point P2, the positions of the light source 11, the light receiving element 12, the measurement object 2, and the reflection pattern 20 do not need to be fixed. This is because even if the position of any of them (for example, the measurement object 2) changes, analysis of the change in position is not necessary to identify the coordinates of the turning point P2.

[0039] When the same light beam LB is used to measure the time of flight and to identify the coordinates of the turning point P2, it is also possible to measure, for example, the shape of the mirror surface 2a of the moving measurement object 2. Furthermore, when the same light beam LB is used to measure the time of flight and to identify the coordinates of the turning point P2, it is also possible to measure the shape of the mirror surface 2a that is fluctuating due to, for example, temperature changes.

[0040] A method for manufacturing a glass sheet according to one embodiment will be described with reference to Fig. 4. The method for manufacturing a glass sheet includes bending a glass sheet (step S101) and measuring the shape of the mirror surface of the bent glass sheet (step S102).

[0041] The bending of the glass sheet (step S101) is performed on the glass sheet in a state where it has been softened by heating. The bending method may be a gravity method or a press method. In the gravity method, the glass sheet is bent by its own weight while a temperature distribution is applied to the glass sheet. In the press method, the glass sheet is bent by pressing it against a mold. After bending, the glass sheet is slowly cooled to reduce distortion.

[0042] The measurement of the shape of the mirror surface of the glass sheet (step S102) is performed using a mirror surface shape measuring device 1 shown in Figures 1 to 3. The mirror surface shape measuring device 1 measures the shape of the mirror surface of the bent glass sheet.

[0043] A bent glass plate is an example of the measurement object 2. The shape of the measurement object 2 is not limited to a plate shape, and may be, for example, a block shape. Furthermore, the material of the measurement object 2 is not limited to a transparent material, and may be an opaque material such as metal. The measurement object 2 may be any material as long as it has a mirror surface 2a.

[0044] The mirror surface shape measuring device, mirror surface shape measuring method, and plate glass manufacturing method according to the present disclosure have been described above, but the present disclosure is not limited to the above-described embodiments. Various changes, modifications, substitutions, additions, deletions, and combinations are possible within the scope of the claims. These naturally fall within the technical scope of the present disclosure.

[0045] This application claims priority based on Japanese Patent Application No. 2024-087319, filed May 29, 2024, the disclosure of which is incorporated herein in its entirety by reference.

[0046] REFERENCE SIGNS LIST 1 mirror surface shape measuring device 2 measurement object 2a mirror surface 10 distance measuring device 11 light source 12 light receiving element 13 control circuit 20 reflection pattern P1 reflection point P2 turning point

Claims

1. A mirror shape measuring device for measuring the shape of a mirror surface of a measurement object that specularly reflects light rays of a predetermined wavelength, comprising: a distance measuring device having a light source that irradiates the light rays toward multiple reflection points on the mirror surface, multiple light receiving elements that receive the light rays returning from the multiple reflection points, and a control circuit that controls the light source and creates an image according to the light receiving intensity of each of the light receiving elements; and a reflection pattern that is positioned at a distance from the mirror surface and diffusely reflects the light rays specularly reflected at the multiple reflection points toward the multiple reflection points, wherein the control circuit: measures the time of flight (ToF) of the light rays from the light source, passing through the mirror surface, the reflection pattern, and the mirror surface in this order, to each of the light receiving elements; creates an image showing the coordinates of the reflection pattern reflected on the mirror surface and identifies the coordinates of the turning points of the light rays in the reflection pattern; and identifies the coordinates of the reflection points for each path of the light rays received by each of the light receiving elements.

2. The mirror surface shape measuring device according to claim 1, wherein the reflection pattern is provided on a substrate that specularly reflects the light beam, and the control circuit creates a time-of-flight image that represents the distribution of the time-of-flight as the image used to identify the coordinates of the turning point.

3. The mirror surface shape measuring device according to claim 1, wherein the reflection pattern is provided on a substrate that diffusely reflects the light beam, and the control circuit creates a light intensity image representing the distribution of the light intensity of a second light beam received by the light receiving element, separate from the light beam used to measure the time of flight, as the image used to identify the coordinates of the turning point.

4. A mirror surface shape measuring device as described in claim 3, wherein the positions of the light source, the light receiving element, the object to be measured, and the reflection pattern are fixed when the first light beam is received and when the second light beam is received.

5. A method for measuring the shape of a mirror surface of an object that specularly reflects light rays of a predetermined wavelength, comprising: preparing a distance measuring device having a light source that irradiates the light rays toward multiple reflection points on the mirror surface and multiple light receiving elements that receive the light rays returning from the multiple reflection points; preparing a reflection pattern that is positioned at a distance from the mirror surface and that diffusely reflects the light rays specularly reflected from the multiple reflection points toward the multiple reflection points; measuring the time of flight (ToF) of the light rays from the light source, passing through the mirror surface, the reflection pattern, and the mirror surface in this order, to each of the light receiving elements; creating an image that represents the coordinates of the reflection pattern reflected on the mirror surface, and identifying the coordinates of the turning points of the light rays in the reflection pattern; and identifying the coordinates of the reflection points for each path of the light rays received by each of the light receiving elements.

6. The mirror surface shape measurement method according to claim 5, wherein the reflection pattern is provided on a substrate that specularly reflects the light beam, and the mirror surface shape measurement method creates a time-of-flight image that represents the distribution of the time-of-flight as the image used to identify the coordinates of the turning point.

7. The mirror surface shape measurement method according to claim 5, wherein the reflection pattern is provided on a substrate that diffusely reflects the light beam, and the mirror surface shape measurement method creates a light intensity image representing the distribution of the light intensity of a second light beam received by the light receiving element, separate from the light beam used to measure the time of flight, as the image used to identify the coordinates of the turning point.

8. A mirror surface shape measurement method according to claim 7, wherein the positions of the light source, the light receiving element, the object to be measured, and the reflection pattern are fixed when the first light ray is received and when the second light ray is received.

9. A method for manufacturing glass sheets, comprising: bending a glass sheet; and measuring the shape of the mirror surface of the bent glass sheet, the method comprising: preparing a distance measuring device having a light source that irradiates light rays of a predetermined wavelength toward a plurality of reflection points on the mirror surface, and a plurality of light receiving elements that receive the light rays returning from the plurality of reflection points; preparing a reflection pattern that is arranged at a distance from the mirror surface and that diffusely reflects the light rays specularly reflected from the plurality of reflection points toward the plurality of reflection points; measuring the time of flight (ToF) of the light rays from the light source, passing through the mirror surface, the reflection pattern, and the mirror surface in this order, to each of the light receiving elements; creating an image that represents the coordinates of the reflection pattern reflected on the mirror surface, and identifying the coordinates of the turning points of the light rays in the reflection pattern; and identifying the coordinates of the reflection points for each path of the light rays received by each of the light receiving elements.

10. A method for producing glass plates according to claim 9, wherein the reflective pattern is provided on a substrate that specularly reflects the light rays, and the method for producing glass plates further comprises creating a time-of-flight image representing the distribution of the times of flight as the image used to identify the coordinates of the turning points.

11. The method for manufacturing a plate glass according to claim 9, wherein the reflection pattern is provided on a substrate that diffusely reflects the light beam, and the method for manufacturing a plate glass further comprises creating, as the image used to identify the coordinates of the turning point, a light intensity image that represents the distribution of the light intensity of a second light beam received by the light receiving element, separate from the light beam used to measure the time of flight.

12. The method for manufacturing a glass sheet according to claim 11, wherein the positions of the light source, the light receiving element, the glass sheet, and the reflection pattern are fixed when receiving the light beam and when receiving the second light beam.

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