Non-contact online melting traction glass thickness measuring system and method

Abstract

A system for measuring the thickness of glass includes: a laser emitting a laser beam through the glass; a sensor sensing an interference pattern of the laser beam passing through the glass; and a computer processing sensor data corresponding to the interference pattern received from the sensor to determine the thickness of the glass.

Description

Technical Field

[0001] Cross-reference to related applications

[0002] This application claims the priority benefit of U.S. Provisional Application No. 63 / 352,725 filed on June 16, 2022 under the Patent Law. This article relies on the contents of the U.S. Provisional Application and the contents of the U.S. Provisional Application are incorporated herein by reference in their entirety.

[0003] The present disclosure relates generally to systems and methods for measuring glass thickness, and more particularly, to in-line systems and methods for measuring the thickness of a moving glass sheet without contacting the moving glass sheet. Background Art

[0004] Glass substrates are commonly used to manufacture a variety of electronic devices, including electronic displays, such as liquid crystal displays (LCD) and organic light-emitting displays (OLED). Electronic displays are provided in devices such as smartphones, tablet computers, laptops, desktop computer monitors, and televisions. As the performance and demand for such devices increase, the demand for efficient mass production of high-quality glass substrates for manufacturing such devices also increases. Thin glass substrates are typically manufactured using a down-draw process such as a fusion-draw process. The continuous glass ribbon produced by the fusion-draw process has superior surface flatness and smoothness compared to glass ribbons produced by other methods. The continuous glass ribbon can be cut into glass sheets and then used as a substrate to be processed into electronic devices.

[0005] While the fusion-draw process forms thin glass sheets with desirable surface properties, the thickness of the glass sheets can be difficult to control, particularly as the glass sheets become thinner. As a result, glass sheet manufacturers are continually improving their glass manufacturing processes and systems so that they can produce glass sheets that meet the performance needs of electronic display manufacturers, who desire glass sheets with increased size and quality at reduced thicknesses.

[0006] As a result, online thickness measurements become increasingly difficult to perform as the size of the glass sheets increases and the overall thickness of the glass sheets decreases. Both of these factors cause a certain amount of variation in the position and / or angular orientation of the glass sheets during manufacturing and affect the accuracy of online thickness measurements.

[0007] Glass thickness measurement is necessary in molten glass production for quality control and as feedback for process control. This requires online measurement in order to react quickly to the production process and remove substandard or bad products from further processing. Thickness measurement can be performed immediately after the glass ribbon has been separated into individual glass sheets using a suitable system. The measurement is performed while the glass sheets are being transported in a direction perpendicular to the vertical molten haul. Due to the influence of the environment and the inherent unevenness of the glass sheets, the glass sheets undergo elastic shape deformations. The deformation changes the distance between the thickness measuring sensor and the measuring point on the glass sheet. In order to keep the distance of the measuring sensor or stylus as a thickness measuring sensor physically touching the glass sheet within the operating range, the glass sheet or sensor position must be kept within a predetermined range from the measuring sensor.

[0008] Contact of glass handling components with the glass sheet is usually made at the edge outside the usable area to minimize damage to the usable area. However, any contact may result in glass breakage. The current trend towards increasing glass flow and reducing glass thickness makes this issue even more important. Reducing glass breakage is now considered one of the main factors in reducing production costs.

[0009] Another method described in USPG Pub. 2012 / 0127487 uses an optical measurement technique with a movable platform to track glass measurement points as the glass is conveyed. In this technique, an edge detector is used to determine an initial spacing distance between a leading edge of a first surface plane of the glass sheet and an optical measurement head as the glass sheet is conveyed in a conveying direction. Using the value of the spacing distance, a control unit adjusts the position of the optical measurement head relative to the first surface plane of the glass sheet so that the first surface plane is within the working range of the optical measurement head. However, it has been found that this technique has the problem of difficulty in accurately determining the leading edge of the glass sheet and is relatively costly.

[0010] Therefore, there is a need for alternative methods and apparatus for in-line thickness measurement of glass sheets during manufacturing that are tolerant of variations in glass sheet size, position, and orientation. Summary of the invention

[0011] Conventional glass sheet thickness measurement methods using optical sensors require the glass sheet to be contained within a limited working range, which can lead to undesirable glass breakage. The disclosed method is non-contact and does not require additional glass motion restraints.

[0012] To overcome the problems described above, embodiments of the present disclosure address the measurement range limitation by utilizing interference of coherent light (i.e., from a laser) propagating through a glass sheet with a portion of incident light that passes through the glass sheet three times. After the incident laser light passes through the front surface, it is partially reflected from the rear surface, partially reflected from the front surface, and then exits the glass from the rear surface. The laser light propagating along these two paths produces an interference fringe pattern on the imaging sensor. The phase unraveling problem of the interference fringe pattern can be solved by using a line scanning sensor that diverges a beam in a plane perpendicular to the motion of the conveyor and produces a virtual collimated beam in the direction of motion of the glass. The increased measurement working range eliminates the need to maintain a strict limit on the distance between the glass sheet and the measurement sensor, and the glass breakage that this may cause. In addition, this method can output a thickness map instead of the conventional single thickness trace. A system including a multi-line scanning sensor can be used to measure a complete sheet thickness map.

[0013] Through the disclosed phase untangling method, interferometric non-contact online thickness measurement is made possible by using the specific properties of the molten-drag glass and a special coherent beam shape.

[0014] In one embodiment, a system for measuring glass thickness includes: a laser that emits a laser beam that passes through the glass; an imaging sensor that senses an interference pattern of the laser beam that passes through the glass; and a computer that processes sensor data corresponding to the interference pattern received from the sensor to determine the thickness of the glass.

[0015] In one aspect, the glass can be a glass sheet.

[0016] The system may further include a transport system for transporting the glass sheet between the laser and the sensor.

[0017] In one aspect, the imaging sensor can be an optical line scan sensor.

[0018] The system may further include a bandpass filter located between the glass and the sensor.

[0019] The system may further include a plurality of lasers, each laser transmitting a corresponding laser beam through the glass to a corresponding imaging sensor.

[0020] In an embodiment, a method for measuring glass thickness includes: passing a glass sheet between a laser and an imaging sensor in a horizontal direction, the imaging sensor sensing an interference fringe pattern of laser light emitted from the laser and passing through a portion of the glass; capturing sensor data of the laser light from the imaging sensor by a computer; locating a saddle and a focus position by analyzing the sensor data by a computer; normalizing the sensor data by a computer; calculating the normalized sensor data as an arccosine; obtaining a reference thickness value of the glass; and calculating the absolute thickness of the glass in the horizontal direction using the reference thickness value.

[0021] The method may further include calculating a vertical thickness gradient of the glass, wherein the vertical thickness gradient is calculated as follows:

[0022] Where S is the distance from the laser to the sensor, S1 is the distance from the laser to the glass, n is the refractive index of the glass, and Δy is the vertical displacement of the sensor plane of the focal center or saddle point.

[0023] In one aspect, normalizing the sensor data includes identifying a maximum value and a minimum value of the sensor data and transforming the sensor data such that the maximum value is equal to 1 and the minimum value is equal to -1.

[0024] In one aspect, the absolute thickness of the glass is calculated by adding a constant so that the thickness at a reference point is equal to a reference thickness value.

[0025] In an embodiment, a non-transitory computer-readable medium including executable instructions, when executed by a processor, causes the processor to perform a method comprising: capturing sensor data of laser light that causes an interference fringe pattern when passing through glass and incident on an imaging sensor; analyzing the sensor data to locate a saddle and a focus position; normalizing the sensor data; calculating the normalized sensor data as an arccosine; and calculating the absolute thickness of the glass along a horizontal direction using a reference thickness value of the glass.

[0026] In one aspect, the method can further include calculating a vertical thickness gradient of the glass.

[0027] In the non-transitory computer readable medium, the vertical thickness gradient is calculated as follows: where S is the distance from the laser to the sensor, S1 is the distance from the laser to the glass, n is the refractive index of the glass, and Δy is the vertical displacement of the center of focus or saddle point on the sensor plane.

[0028] In the non-transitory computer readable medium, normalizing the sensor data includes identifying a maximum value and a minimum value of the sensor data and transforming the sensor data such that the maximum value is equal to 1 and the minimum value is equal to -1.

[0029] In the non-transitory computer readable medium of claim 12, wherein the absolute thickness of the glass is calculated by adding a constant so that the thickness at the reference point is equal to the reference thickness value.

[0030] The above and other features, elements, characteristics, steps and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the present invention with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 and Figure 2 A glass thickness measurement system according to an embodiment of the present disclosure is presented.

[0032] Figure 3 Laser light from the same source is shown propagating through a glass plate.

[0033] Figure 4 It is an image of a striped pattern.

[0034] Figure 5 is a graph showing the theoretical perceived (effective) glass thickness variation versus distance from the middle of the optical sensor for a 0.5 mm glass sheet.

[0035] Figure 6 A glass thickness measurement system according to another embodiment of the present invention is presented.

[0036] Figure 7 4 is a flow chart of a non-contact thickness measurement method of a glass plate according to an embodiment of the present invention.

[0037] Figure 8 is an example of an interference fringe pattern for thickness measurement using the disclosed method.

[0038] Fig. 9 is a graph comprising thickness measured by the disclosed method on a 250 mm long glass sheet and three independent measurements made using separate measuring sensors. DETAILED DESCRIPTION

[0039] Figure 1 and Figure 2 A system for measuring glass thickness is presented. In an embodiment of the system, Figure 1 and Figure 2 Exemplary orientations of imaging optical line scan sensor 10 and laser 20 relative to the transport motion of glass sheet 30 are shown. Figure 1 1 is a front view of the optical line scanning sensor 10. Figure 1 As shown, the glass sheet 30 moves along the X direction, which is shown as from left to right. Figure 2 is a side view showing a glass sheet 30 moving between lasers 20, wherein emitted radiation is directed through the glass sheet 30, through an optional bandpass filter 40 and to an optical line scan sensor 10 having a sensor surface lying in the XY plane. The lasers 20 may be configured to emit a radiation pattern 15 covering a sensor line 17. Figure 2As shown, the optical sensor 10 can be connected to a frame acquisition card in a computer 50, which can include a memory for storing sensor data read by the frame acquisition card and performing thickness calculations. The computer 50 can be any suitable configuration, including a computer or a computer / processor network with a processor that can store sensor data and perform thickness calculations as described below.

[0040] Figure 2 is a side view showing glass plate 30 moving in the X direction perpendicular to the page, wherein laser 20 is located on one side of glass plate 30, opposite optical line scan sensor 10 on the other side of glass plate 30. Although any suitable distance is possible, laser 20 may be 700±500 mm away from glass plate 30, and optical sensor 10 may be 150 mm±100 mm away from glass plate 30.

[0041] Figure 3 Laser light from the same source is shown propagating through the glass sheet 35 in the yz plane. The solid backward arrow represents a portion of the laser light incident at a certain angle, which passes through the glass sheet 35 three times, reflects from the back surface (relative to the laser), and then reflects from the front surface. The thinner dashed arrow represents the light that is not internally reflected and is transmitted through the surface of the glass sheet. The thick dashed arrow represents a portion of the light from the laser incident at a certain angle, which passes through the glass sheet 35 once without internal reflection. As a result, the internally reflected light and the light that does not reach the optical sensor are out of phase with each other. This phase difference will determine the light intensity at this point, which is used to calculate the thickness of the glass sheet.

[0042] like Figure 2 As shown in Figure 1, the laser beam diverges in the vertical direction (yz plane), and the incident angle of the light to the glass sheet increases with the distance away from the normal. For a 0.5 mm flat glass sheet, the theoretically perceived (effective) glass thickness decreases with the distance from the middle of the optical sensor, as shown in Figure 1. Figure 5 This produces a graph like Figure 4 The vertical thickness stripes shown in Figure 1. In the horizontal direction, the laser beam is almost perpendicular to the glass plate and can be considered to be collimated in this direction. This condition is beneficial for phase unraveling calculations. If the stripes are formed as Figure 4 If the glass thickness gradient is a pie pattern as shown in the center part of the image (here called the focus), the glass thickness gradient has the same sign in all directions. Since we know that the effective thickness in the vertical direction is the largest at the normal, the actual thickness in the horizontal x direction will also have the maximum value. If it is a cross pattern (here called a saddle), the thickness at this point is the smallest in the x direction. Figure 4 The black curve in the figure represents the thickness distribution in the horizontal direction.

[0043] Figure 6A system for measuring glass thickness according to another embodiment of the present disclosure is shown. Figure 6 In the system of FIG. 1 , multiple lasers 20 may be used to emit corresponding laser beams through the glass sheet 30 to provide interference patterns to corresponding optical line scan sensors 10. The optical line scan sensors 10 may be connected to transmit sensor data to a computer 50 including a memory that stores and processes the sensor data to determine the thickness across several portions of the glass sheet 30. Although Figure 6 , three lasers 20 and three optical line scan sensors 10 are shown, but any suitable number of lasers 20 and corresponding optical line scan sensors 10 may be incorporated into the system. In alternative aspects of the present disclosure, multiple lasers 20 may be used to provide interference patterns to one optical line scan sensor 10. The beams from the sources may overlap in the vertical direction and be placed in a staggered configuration in the x-direction to minimize or prevent light leakage from adjacent sources.

[0044] Figure 7 1 is a flow chart of a non-contact thickness measurement method for a glass sheet according to an embodiment of the present invention. In the embodiment, in step S1, the glass sheet passes between a laser and an optical line scanning sensor, such as Figure 1 and Figure 2 The sensor data is captured and processed by a computer.

[0045] In step S2, the saddle and focus positions of the interference fringe pattern are found in the sensor data. The interference fringe pattern is analyzed by searching for these patterns in the fringe image to find the saddle and focus positions, as described below. They will determine the increase and decrease in horizontal thickness for a given segment, for example, Figure 4 shown.

[0046] In step S3, the fringe oscillation is normalized. The regional minimum and maximum are found, and a linear transformation is performed on each segment so that the maximum value is equal to 1 and the minimum value is equal to -1.

[0047] In step S4, the phase of the oscillating normalized signal is calculated as arc cosine. In this step, the value of the phase before unraveling ranges from 0 to π. This is referred to as the initial stage.

[0048] In step S5, phase disentanglement is performed using the thickness decrease / increase information from step S2. For example, at one of the maximum thicknesses, the disentangled phase is set to 0. The disentangled phase will decrease to the point where the initial phase reaches the value π, assuming that the following minimum value has not yet been reached. After this, the unsolved phase will start from the value it reached and continue to decrease until the minimum value is reached. The disentanglement process then continues to the next maximum value. Over this section, the disentangled phase will increase. When such disentanglement process is completed in both directions starting from the initial point, the relative glass thickness d0(x) has been obtained as

[0049]

[0050] Where λ is the laser wavelength, is the unravelled phase, and n is the refractive index of the glass.

[0051] In step S6, at least one reference thickness measurement made with a different instrument (e.g., using a sensor contacting the glass) is used to establish an absolute thickness distribution. For example, if the reference thickness value d(x1)=r1 obtained by an independent measurement at a reference point x1, then the absolute thickness at any point x is calculated as

[0052] d(x)=C+d0(x),

[0053] where the constant C is given by:

[0054] C = r1-d0(x1).

[0055] If there are multiple reference thickness points available, the constant can be obtained, for example, by minimizing the sum of squares of thickness deviations of all reference points.

[0056] The reference thickness measurement can be obtained by placing an independent thickness gauge at a fixed position where the glass sheet will be within the working range of the thickness gauge at least once when the glass sheet is transported through the fixed position. Alternatively, the independent thickness gauge can be positioned on a platform that oscillates in the z-direction so that the glass sheet is within the working range of the sensor at least once during the transport. In terms of time, step 6 can occur simultaneously with step 1, or even before step 1.

[0057] Optionally, step S7 may be included to find the vertical position on the focus / saddle point and calculate the vertical thickness gradient. To calculate an estimate of the vertical thickness gradient, the vertical displacement Δy of the focus center and the saddle point in the sensor plane must be extracted from the fringe pattern using appropriate image processing methods. The thickness gradient x in the vertical direction at this point is then calculated as follows:

[0058]

[0059] where S is the distance from the laser to the sensor, S1 is the distance from the laser to the glass, n is the refractive index of the glass, and Δy is the vertical displacement of the focal center or saddle point in the sensor plane. Alternatively, using the same phase untangling method as described above, the vertical effective untangled phase is calculated as where θ is the angle of incidence in the yz plane.

[0060] The remaining calculations are performed similarly to the horizontal distribution calculations. By repeatedly calculating a set of x positions and converting the incident angles to vertical glass positions, a thickness map d(x,y) can be obtained.

[0061] Figure 8 is an example of an interference fringe pattern for thickness measurement using the disclosed optical system. Figure 8 An example of a fringe pattern is shown for glass having an actual thickness of approximately 0.48 mm over a length of 250 mm.

[0062] Fig. 9 is a comparison of the thickness d(x) measured on a 250 mm long glass plate by the disclosed method (solid curve) and an independent measurement (dashed curve) using a Keyence SI-F80 measurement sensor. The Keyence SI-F80 is a confocal thickness gauge. Fig. 9 It was shown that the deviation of the reconstructed distribution using the disclosed measurement method is about 0.2 μm, which is within the variation of three measurements performed using the SI-F80 measuring instrument.

[0063] Optionally, when the vertical thickness gradient is less than the horizontal gradient, a reference thickness measurement may also be obtained from the vertical fringe pattern. This would eliminate the need to use a separate instrument to obtain a reference thickness measurement. The feasibility of an absolute measurement would depend on the noise in the fringe pattern.

[0064] The embodiments described above of the present disclosure may be implemented in any of a number of ways. For example, the embodiments may be implemented using hardware, software, or a combination thereof. When implemented in software, the software code may be executed on any suitable computer or collection of processors, whether provided in a single computer or distributed among multiple computers. Such processors may be implemented as integrated circuits, with one or more processors in an integrated circuit component. However, the processor may be implemented using circuits of any suitable format.

[0065] Additionally or alternatively, the embodiments described above may be implemented as a non-transitory computer-readable storage medium on which a program executable by a processor that performs the methods of the various embodiments is embodied.

[0066] In addition, the various methods or processes outlined herein may be programmed as software that can be executed on one or more processors that employ any of a variety of operating systems or platforms. In addition, such software may be written using any of a number of suitable programming languages ​​and / or programming or scripting tools, and may also be compiled into executable machine language code or intermediate code that executes on a framework or virtual machine. In general, the functionality of program modules may be combined or distributed as desired in various implementations.

[0067] In addition, embodiments of the present disclosure may be embodied as a method, examples of which have been provided. The actions performed as part of the method may be ordered in any suitable manner. Thus, embodiments may be constructed in which the actions may be performed in an order different from the order illustrated, and such embodiments may include performing some actions simultaneously, although such actions are shown as sequential actions in the exemplary embodiments.

[0068] It should be understood that the foregoing description is merely an illustration of the present invention. A person skilled in the art may devise various substitutions and modifications without departing from the present invention. Therefore, this specification is intended to cover all such substitutions, modifications and variations falling within the appended claims.

Claims

1. A system for measuring the thickness of glass, the system comprising: a laser that emits a laser beam that passes through the glass; an imaging sensor that senses an interference pattern of the laser beam passing through the glass; and A computer processes sensor data corresponding to the interference pattern received from the sensor to determine the thickness of the glass.

2. The system of claim 1, wherein the glass is a glass sheet.

3. The system of claim 2, further comprising a conveying system for conveying the glass sheet between the laser and the sensor.

4. The system of claim 1, wherein the imaging sensor is an optical line scan sensor.

5. The system of claim 1, further comprising a bandpass filter located between the glass and the sensor.

6. The system of claim 1, further comprising a plurality of lasers, each laser transmitting a corresponding laser beam through the glass to a corresponding imaging sensor.

7. A method for measuring the thickness of glass, the method comprising: Passing a glass plate between a laser and an imaging sensor in a horizontal direction, the imaging sensor sensing an interference fringe pattern of laser light emitted from the laser passing through a portion of the glass; capturing, by a computer, sensor data of said laser light from said imaging sensor; Analyzing the sensor data by the computer to locate the saddle and focus position; normalizing the sensor data by the computer; calculating the normalized sensor data as an arc cosine; Obtaining a reference thickness value of the glass; as well as The reference thickness value is used to calculate the absolute thickness of the glass along the horizontal direction.

8. The method of claim 7, further comprising: calculating a vertical thickness gradient of the glass.

9. The method of claim 8, wherein the vertical thickness gradient is calculated as: Where S is the distance from the laser to the sensor, S1 is the distance from the laser to the glass, n is the refractive index of the glass, and Δy is the vertical displacement of the focal center or saddle point on the sensor plane.

10. The method of claim 7, wherein normalizing the sensor data comprises: A maximum value and a minimum value of the sensor data are identified and the sensor data is transformed so that the maximum value is equal to 1 and the minimum value is equal to -1.

11. The method of claim 7, wherein the absolute thickness of the glass is calculated by adding a constant so that the thickness at a reference point is equal to a reference thickness value.

12. A non-transitory computer-readable medium comprising executable instructions that, when executed by a processor, cause the processor to perform a method comprising: capturing sensor data of laser light causing an interference fringe pattern when passing through glass and incident on an imaging sensor; analyzing the sensor data to locate saddle and focus positions; normalizing the sensor data; calculating the normalized sensor data as an arc cosine; as well as The absolute thickness of the glass along the horizontal direction is calculated using the reference thickness value of the glass.

13. The non-transitory computer readable medium of claim 12, wherein the method further comprises: calculating a vertical thickness gradient of the glass.

14. The non-transitory computer readable medium of claim 13, wherein the vertical thickness gradient is calculated as: Where S is the distance from the laser to the sensor, S1 is the distance from the laser to the glass, n is the refractive index of the glass, and Δy is the vertical displacement of the sensor plane of the focal center or the saddle point. 15 . The non-transitory computer-readable medium of claim 12 , wherein normalizing the sensor data comprises identifying a maximum value and a minimum value of the sensor data and transforming the sensor data such that the maximum value is equal to 1 and the minimum value is equal to −1.

16. The non-transitory computer readable medium of claim 12, wherein the absolute thickness of the glass is calculated by adding a constant so that a thickness at a reference point is equal to the reference thickness value.

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