JP2022532609A - Systems and methods for performing edge strength tests with real-time stress visualization on ultrathin glass panels - Google Patents

Abstract

An apparatus for testing sheets of brittle material is disclosed. The apparatus includes a plurality of assemblies that apply a load to an area of a sheet of material and takes measurements on the surface of the area without load and with load on the surface of the area while the area is loaded. It may include a direct acquisition sensing mechanism and a processor that analyzes the no-load measurements and the loaded measurements to determine the stresses caused by the loading of the load. This device can rely on direct optical imaging of the sheet being evaluated. A method for testing sheets of brittle material in both static and dynamic modes is also disclosed.

Description

Explanation of related applications

This application is based on its contents and is cited in its entirety here. It claims the benefits of rights.

The present disclosure generally relates to devices for testing glass and / or glass ceramics, and methods for testing glass and / or glass ceramics.

High performance display devices such as liquid crystal displays (LCDs) and plasma displays are commonly used in a variety of electronic devices such as mobile phones, laptops, electronic tablets, televisions and computer monitors. Display devices currently on the market may have one or more precision glass sheets used, for example, as substrates for electronic circuit components or as color filters, to name a few. An advanced technique for manufacturing such a high-quality glass substrate is a fusion drawing method developed by Corning Inc., for example, described in Patent Document 1 and Patent Document 2. The contents of these documents are incorporated and all are cited here. However, the embodiments described herein are applicable to any forming method including slot draw method, redraw method, float method and the like.

US Pat. No. 3,338,696 US Pat. No. 3,682,609

For each of these applications, the glass sheet is typically cut to a predetermined size, and the sharp edges of the cut glass sheet are chamfered by grinding and / or polishing. Cutting, edge machining, grinding and other processing steps can cause defects such as chipping or cracking on the surface and edges of the glass sheet. Such defects can be a source of fracture and reduce the strength of the glass sheet, especially if the glass is bent to the extent that the defects are subjected to tensile stress. Since display devices are subject to some degree of bending, the presence of such defects may be a concern. Due to the nature of flexible display devices, large stresses may be generated on the display substrate either during the manufacturing process or during use. Therefore, defects that may be present in the glass can be stressed sufficiently large enough to break the glass. A typical display manufacturing process involves cutting the glass to form an individual display, and the cutting process is known to cause multiple defects in the glass along the cutting edges, thus a glass substrate. Flexible display devices using the above may be more likely to be damaged.

Attempts to mitigate defects at the edges of glass sheets include laser cutting, grinding, polishing, etc., all of which are attempts to eliminate or minimize defects that occur when the glass sheet is cut to a given size. .. However, many of these approaches are technically difficult to remove because they cannot remove defects until they are sized to accommodate the expected stresses, or are difficult to apply to thin glass sheets (thickness less than about 0.4 mm). Therefore, it is insufficient. The glass edge may be etched with an acid, but this treatment may deteriorate the display device arranged on the substrate. As such, defects continue to form on glass sheets, especially on the edges of the sheets, so it is necessary in the industry to accurately test the edge strength of such glass sheets and panels or laminated structures using glass sheets. ing.

An exemplary embodiment describes a method of continuously measuring the fracture strength of a glass edge by applying stress to the edge, where the stress at a site away from the edge is greater than the fracture strength at its respective position. Remarkably low. Further, using an exemplary embodiment, both sides of the edge can be exposed to substantially the same tensile stress during the measurement. Further, in the exemplary embodiment, the processing speed is at least 30 times higher, the amount of edges to be tested is at least 3 times higher, and the amount of sheet to be tested after processing is increased as compared with the conventional method. Provides continuous high-speed processing with orders of magnitude higher. Therefore, such an increase in the number of statistical samplings can ensure that the shipment of defective products to customers is reduced, and is suitable for online configurations.

In some embodiments, equipment for testing material sheets is provided. This device provides multiple assemblies that load a region of a material sheet, unloaded measurements on the surface of that region, and loaded on that surface of the region while the region is loaded. It can include a detection mechanism that directly acquires the measured values and a processor that analyzes the unloaded and loaded measurements to determine the stress caused by the load. In some embodiments, the load causes bending in the area of the material sheet.

In other embodiments, a method of testing a material sheet is provided. This method involves providing a material sheet, acquiring unloaded measurements on the surface of the sheet area, applying a load to the sheet area, and loading the surface of the sheet area. It is possible to include a step of acquiring the measured value of the above and a step of determining the stress caused by the load of the load based on the measured value with no load and the measured value with a load. In some embodiments, the devices described herein can be used to carry out such methods.

Further features and advantages of the present disclosure are described in the detailed description below, in part which will be readily appreciated by those skilled in the art from that description, or the detailed description below, the scope of patent claims and the accompanying drawings. Will be recognized by those of skill in the art by performing the methods described herein.

Both the above overview and the detailed description below present various embodiments of the present disclosure and are intended to provide an overview or framework for understanding the nature and characteristics of the claims. Please understand that there is. The accompanying drawings are included to provide a further understanding of the present disclosure, are incorporated herein by reference, and form part of this specification. These drawings show various embodiments of the present disclosure and are used to illustrate the principles and actions of the present disclosure, along with a detailed description.

The following detailed description is best understood when read in conjunction with the following drawings, in which, where possible, similar structures are given similar reference numerals.
Diagram showing an exemplary glass manufacturing system The figure which shows the change of the load and stress on the tension side with the change of the adhesive part between panels. The figure which shows the change of the load and stress on the tension side with the change of the roller contact. Schematic diagram showing the position and load of a support in one embodiment of the apparatus disclosed herein. Figure showing material sheet before and during deformation (loading), as well as area tracking Isometric view of an embodiment of the apparatus disclosed herein. Side view of the device of FIG. Top view of the device of FIG. Perspective side view of an image showing an arrangement configuration of one assembly in contact with a material sheet as disclosed herein. Top view of the material sheet in the arrangement configuration of FIG. 9A Diagram of stress field of sample obtained when load is 6N The figure which shows the maximum stress in the test in a static mode A diagram comparing the results of a stress field generated using a digital image correlation (DIC) apparatus disclosed herein with a stress field generated using a finite element analysis (FEA). Diagram of the relationship between maximum stress and displacement calculated using the digital image correlator and finite element analysis disclosed herein. Schematic diagram showing dynamic modes of the apparatus disclosed herein. Schematic diagram showing the order of regions imaged as a material sheet passes through multiple assemblies in the absence of a load. Schematic diagram showing the order of regions imaged as a material sheet passes through multiple assemblies under load. Figure of stress map of digital image correlation method when the load is 11N consisting of 60 steps It is a stress map under the same test conditions consisting of only one step, and it is confirmed that it is the same as the stress map of the digital image correlation method. First schematic of the sample sequence used for calibration (top) and plan view of the sheet shown in the schematic (bottom) A second schematic of the sample sequence used for calibration (top) and a plan view of the sheet shown in the schematic (bottom). A third schematic of the tilted sample array used for calibration (top) and a plan view of the sheet shown in the schematic (bottom). Fourth schematic of the tilted sample array used for calibration (top) and plan view of the sheet shown in the schematic (bottom) Schematic of a belt roller that may be used in the embodiments disclosed herein. Schematic of a ball roller that may be used in the embodiments disclosed herein.

FIG. 1 schematically illustrates a glass manufacturing system 100 for manufacturing a glass ribbon 104, such as a glass ribbon of interest, for which the devices and methods disclosed herein are designed to be evaluated. The glass manufacturing system 100 includes a melting tank 110, a melting / clarification pipe 115, a clarification tank (for example, a clarification pipe) 120, a clarification / stirring tank connecting pipe 125 (including a liquid level probe stand pipe 127 extending from the melting tank), and a mixing tank. (For example, stirring tank (static or dynamic)) 130, stirring tank / bowl connecting pipe 135, sending tank (for example, bowl) 140, descending pipe 145, and charging section 155, forming body (for example, isopipe) 160. And FDM150 including pull roll assembly 165 can be included.

As indicated by the arrow 112, the glass batch material can be charged into the melting tank 110 to produce the molten glass 114. The term "batch material" and variations of that term are used herein to indicate a mixture of glass precursor components that react and / or combine to form glass upon melting. The glass batch material may be prepared and / or mixed by any known method for compounding glass precursor materials. For example, in some non-limiting embodiments, the glass batch material can be, for example, a dry mixture of glass precursor particles free of any solvent or liquid, or a substantially dry mixture. .. In other embodiments, the glass batch material can be in slurry form, eg, a mixture of glass precursor particles in the presence of a liquid or solvent. In various embodiments, the batch material is a glass precursor material such as silica, alumina, and various additional oxidations such as boron oxide, magnesium oxide, calcium oxide, sodium oxide, strontium oxide, tin oxide, or titanium oxide. Can include things. For example, the glass batch material can be a mixture of silica and / or alumina with one or more additional oxides. In various embodiments, the glass batch material is about 45-about 95% by weight of alumina and / or silica in total, boron oxide, magnesium oxide, calcium oxide, sodium oxide, strontium oxide, tin oxide, and / or titanium oxide. At least one of the above is contained in a total of about 5 to about 55% by weight. The clarification tank 120 can be connected to the melting tank 110 by a melting / clarification pipe 115. The clarification tank 120 may have a high temperature treatment region capable of receiving the molten glass from the molten glass 110 and removing air bubbles from the molten glass. The clarification tank 120 can be connected to the clarification tank 130 by the clarification / stirring tank connecting pipe 125. The stirring tank 130 can be connected to the bowl 140 by a stirring tank / bowl connecting pipe 135. The bowl 140 can deliver the molten glass to the FDM 150 via the descending tube 145.

The FDM 150 can include a charging section 155, a forming body 160, and a pull roll assembly 165. The charging section 155 can receive the molten glass from the descending tube 145, and the received molten glass can flow into the forming body 160, where it is formed as a glass ribbon 104. The pull-roll assembly 165 can deliver the stretched glass ribbon 104 for further processing by a further optional device. For example, the glass ribbon can be further processed by a mobile anvil device (TAM), which may include a mechanical scoring device for scoring the glass ribbon. The scored glass is then divided into small pieces of glass sheet, machined, polished, chemically strengthened, and / or other surface treatments using various methods and devices known in the art. , For example, etching, etc. may be applied. Although the process by the fusion method has been described above, the scope of claims accompanying the present specification is not limited to the following, but any method including a slot draw method, a redraw method, a float method, and the like. It should not be so limited as it is applicable to the forming method.

As mentioned above, the glass sheet can typically be cut to a predetermined size, and then during the subsequent finishing process, the sharp edges of the cut glass sheet are chamfered by grinding and / or polishing. Will be done. Edge stress on the glass sheet during such post-finishing, handling or other operating processes can damage the glass sheet and cause serious disruption to the glass production line or the user's production line. there is a possibility. Therefore, after manufacturing, the edge strength may be tested at the manufacturing plant. A conventional method of edge strength test is 4-point vertical bending (V4PTB). V4PTB tests small samples or specimens about 150 mm long and about 10 mm wide. These need to be cut from the manufactured glass sheet and then tested individually. This is a manual intensive method, it takes about a day to process a sample from one sheet, so only a few sheets are tested, for example 22,000 sheets. Each time a product is produced, it becomes about 3 sheets. Moreover, such methods cannot evaluate laminated structures or panels. Such disadvantages can lead to the shipment of seriously defective products in the form of defective products reaching customers.

Conventional techniques for measuring edge stress and edge strength of ultrathin glass sheets using a three-point bending configuration have yielded very variable results. These results are among others: (a) pre-test breakage, (b) residue or dust in the system, (c) product variability (eg, panel thickness, adhesive properties / position changes), and (d). ) Exposed to considerable levels of variability based on various factors, including but not limited to position adjustments. The causes of such variability have resulted in inaccurate strength measurements and unexpected product defects in the market. 2 and 3 show how changes in the bond and roller contact result in variations in stress values. A further cause of variability is the fact that the existing three-point bending configuration provides results based on the glass sheet model, but does not directly measure the surface of the area of the glass sheet being inspected. There is.

In contrast, the measuring devices and methods disclosed herein provide stress distribution in real time using direct image correlation (DIC) full area imaging techniques. Using DIC, it is possible to measure strain in two orthogonal directions in a plane at the same time as a function of time. The stress is determined from the measured strain. The direct measurement techniques disclosed herein are more accurate than conventional techniques, eliminating the need to develop new calibration formulas and models each time the glass sheet is redesigned or reconstructed. Examples of device use described herein include, but are not limited to:
(A) Useful for calibrating currently implemented edge strength testers that do not rely on direct optical measurements;
(B) The flexibility to change various test parameters such as roller contact, panel angle, roller diameter, load factor, etc. is useful for scrutinizing failure modes in the development of new panels;
(C) Useful for making direct optical stress measurements during dynamic and continuous edge strength tests suitable for manufacturing plants.

Examples of advantages and advantages of the devices described herein include, but are not limited to:
-Direct full field (optical) stress measurement of ultra-thin glass panels.
-Optical imaging for detection with full-field stress mapping provides insights on failure modes.
• Visualize stress in real time during dynamic and continuous edge testing suitable for manufacturing plant deployments.
-Improvement of the analysis formula to calculate the stress from the measured strain.
-A new material handling assembly that provides improved optical visibility to enable the above stress measurements.
-Ability to serve as a calibration criterion for existing edge strength test equipment.
-Ability to change test parameters such as roller diameter, contact area, roller thickness to develop new panel designs.
-Accurate stress measurement with an accuracy of ± 5% for the measured stress.

As shown in the figure, in some embodiments, an apparatus 200 for testing a sheet 204 made of a material is provided. The apparatus 200 includes a plurality of assemblies 206 that load the region 208 of the material sheet 204, and unloaded measurements on the surface 212 of the region 208 and the surface 212 of the region 208 while the region 208 is loaded. Includes a detection mechanism 210 that directly obtains the measured values under load and a processor 214 that analyzes the measured values under no load and the measured values under load to determine the stress caused by the load. be able to. In some embodiments, the load causes deformation 216 in region 208 of the material sheet 204.

In some embodiments, the material of the sheet 204 is a brittle material. In some embodiments, the brittle material is glass or glass ceramic. In some embodiments, the load is sufficient to deform region 208 of the material sheet 204. In some embodiments, the plurality of assemblies 206a, 206b include a first assembly 206a comprising one arcuate member 218 for contacting a first side surface of the sheet 204, and a first side surface of the sheet 204. Includes a second assembly 206b that includes two arcuate members 220a, 220b that are spaced apart from each other for contact with a second side surface on the opposite side. The arcuate member is primarily described as a roller, but the arcuate member is a cylindrical roller (FIGS. 11A-11C and 13A-13D), a belt roller (14), and a bearing roller (15). It should be understood that can be selected from a group including, but not limited to.

In some embodiments, for example, FIG. 14, the arcuate members 218, 220a, 220b are belt rollers 238. In an exemplary embodiment, the belts 240a, 240b, 240c can be routed around the drive shafts 242a, 242b, 242c and the arcuate tensioners 244a, 244b, 244c, respectively. In some embodiments, the arcuate tensioner can be a cylindrical roller or a stationary arcuate tensioner (such as a polished metal finger with an arcuate portion for contact with the belt).

In some embodiments, for example, in FIG. 15, the arcuate members 218, 220a, 220b are bearing rollers 246a, 246b, 246c, respectively. In such an embodiment, the bearing rollers 246a, 246b, 246c are formed of rollerballs 248a, 248b, 248c arranged and held in the sockets 250a, 250b, 250c, respectively.

In some embodiments, for example, as shown in FIGS. 10C and 11A, one arcuate member 218 is longitudinally between two arcuate members 220a, 220b spaced apart from each other. Be placed. As used herein, "longitudinal" refers to the direction of movement of the sheet 204 through the test apparatus 200 (eg, the direction of the machine).

In some embodiments, the detection mechanism 210 is arranged to face a second side surface 226 of the sheet 204 and detects a surface between two arcuate members 220a, 220b spaced apart from each other. Includes the optical system 222 of. In some embodiments, the apparatus 200 comprises a static mode in which the first optical system 222 acquires both unloaded and loaded measurements. In the static mode in some such embodiments, the loaded load is increased until a predetermined load is reached or until the destruction of the sheet 204 is detected. In some embodiments, the first optical system comprises at least two cameras to detect deformation of the sheet in measurements under no load and under load.

In some embodiments, the detection mechanism 210 comprises two optical systems 224a, 224b disposed opposite to a second side surface 226 of the sheet, and two arcuate members 220a spaced apart from each other. The surface of the sheet is detected before it advances during 220b. In some embodiments, the second side surface 226 of the sheet 204 is the pulling side of the sheet 204. In some embodiments, as shown in FIGS. 11A, 11B, and 11C, the device 200 comprises a dynamic mode in which the sheet 204 advances longitudinally through a plurality of assemblies 206 and includes a second optical mode. The system 224 acquires the measured values under no load, and the first optical system 222 acquires the measured values under load. In some embodiments, the arcuate members 218, 220a, 220b are rollers, as shown in FIGS. 11A, 11B, and 11C. In some embodiments, the second optical system includes at least two cameras to detect sheet deformation in measurements under load.

In some embodiments, the plurality of assemblies 206a, 206b are configured to allow the sheet 204 to pass longitudinally forward through the plurality of assemblies 206a, 206b, as shown in the order shown in FIGS. 11B and 11C. , Multiple stress measurements are determined continuously or intermittently along the edges of the sheet 204 passing through the multiple assemblies. In some embodiments, the stress is determined in at least two dimensions. In some embodiments, the two-dimensional stress is displayed as a surface plot. Examples of surface plots are those shown in FIGS. 10A, 10C, 12A, and 12B. In some embodiments, the device comprises a display 228 suitable for displaying stress results.

In some embodiments, the pattern pattern 230 on the surface 212 of the region 208 facilitates measurements with no load and with load. In some embodiments, the load of load deforms the surface 212 of the area 208 of the sheet. In some embodiments, the pattern pattern 230 is used to detect the surface during measurements under no load and to detect deformation 216 of the sheet during measurements under load. In some embodiments, the pattern pattern 230 facilitates comparison of unloaded and loaded measurements for alignment purposes. In some embodiments, the pattern pattern 230 is printed on or projected onto the surface 212.

In other embodiments, a method of testing a material sheet is provided. This method involves providing a material sheet, acquiring unloaded measurements on the surface of the sheet area, applying a load to the sheet area, and loading the surface of the sheet area. It is possible to include a step of acquiring the measured value of the above and a step of determining the stress caused by the load of the load based on the measured value with no load and the measured value with a load. In some embodiments, the devices described herein can be used to carry out such methods.

In some embodiments, the load of load deforms the surface of the area of the seat. In some embodiments, in static mode, the first optical system acquires both unloaded and loaded measurements. In some embodiments, the load of the load is increased in static mode until a predetermined load is reached or a sheet breakage is detected.

In some embodiments, the first optical system obtains the measured values under load, the second optical system obtains the measured values under no load, and the measured values at no load are under load. Obtained before the measured value is obtained. Such a configuration is shown at the left end of the schematic diagram of FIG. 11C. In some embodiments, in dynamic mode, the sheet is advanced to pass through the test equipment (eg, longitudinally), with unloaded and loaded measurements on the surface of the region sequentially. And then compared in the process of determination. In some embodiments, the stress is determined in at least two dimensions. Deformation can be measured in all three dimensions, with strain measured in-plane in two orthogonal directions. In some embodiments, the pattern on the surface of the area facilitates measurements with no load and with load.

In some embodiments, the stress is determined by a segmental decomposition of the time axis, i.e., a history of stress changes is obtained. This can be obtained in either a static mode in which the load is gradually increased until the seat is destroyed, or a dynamic mode in which the seat advances through multiple assemblies bearing a given load.

Although some embodiments are described with reference to a sheet 204 made of glass, the claims that accompany this specification are that the test equipment 200 described herein has a laminated structure or It should be noted that it should not be so limited as it can be used for panel acceptance or uptake and analysis. A suitable laminated structure can include a plurality of glass sheets having one or more intermediate polymer layers, or in an alternative embodiment, a structure having a thin film transistor glass substrate and a color filter glass substrate, in between. It can also include structures with one or more films, or structures with one or more films adjacent to one or both substrates. Thus, when reference is made to sheet 204 or glass sheets herein, glass, glass ceramics, plastics, as well as laminated structures and other panels can also be referred to. For the sake of brevity, only Sheet 204 is described herein.

The range of length / width dimensions of the sheet 204 is from about 5 mm / 5 mm to about 100 mm / 100 mm, to about 600 mm / 600 mm, to about 1000 mm / 1000 mm, to about 2300 mm / 2600 mm, to about 4000 mm / 4000 mm, and theirs. It can be any subrange within. The range of length / width dimensions of the glass sheet in the panel or laminated structure is also from about 5 mm / 5 mm to about 100 mm / 100 mm, up to about 600 mm / 600 mm, up to about 1000 mm / 1000 mm, up to about 2300 mm / 2600 mm, about 4000 mm / 4000 mm. Up to, and any subrange within them. Further, adjacent glass sheets in a panel or laminated structure may have different length / width dimensions, in which case one sheet overlaps another and one sheet is of another sheet. It can overlap on one or more sides. Illustratively, the thickness of the glass of each glass sheet contained in one glass sheet or panel or laminated structure is less than 0.1 mm (for example, about 10 micrometer) to more than 5 mm, 0.1 mm to 3 mm, 0. .4 mm to 2 mm, 0.5 mm to 1 mm, 0.5 mm to 0.7 mm may be used.

The table 202 is configured to support the material sheet 204 and can be made of any suitable material including, but not limited to, steel, carbon fiber and the like. The table 202 may include a plurality of drive mechanisms configured to move the glass sheet 204 into place to initiate a measurement cycle or to advance the sheet 204 for continuous testing.

In some embodiments, a predetermined portion of the edge of the sheet 204 is used for testing. In some embodiments, the width range of this predetermined site is from about 1 mm to about 5 mm, from about 1.5 mm to about 3.5 mm, from about 2 mm to about 3 mm, and any partial range within them. Can be. In one embodiment, only the outermost 2 mm of the surface of the glass sheet is in contact with the roller assembly included in the test apparatus 200, ensuring that stress concentration is generated at the edges of the glass sheet and on the surface. Minimize the chance of rolling particles that can cause cracking. When the sheet 204 is a panel or laminated structure whose edge strength is measured and adjacent glass sheets within these panels or laminated structures are different (eg, having the feature that one or more edges of the structure overlap). In, a given site is measured with respect to a smaller glass sheet (ie, a non-overlapping sheet) within the structure.

In some embodiments, each or any arcuate member 218, 220a, 220b of the assembly 206 carries the risk of causing fracture in the sheet 204 during non-destructive testing (eg, not assessing maximum stress). Compliance can be to be minimized. The arcuate member or roller should have sufficient compliance, provide long life to minimize maintenance and downtime, and have sufficient friction to allow the roller to rotate freely on the glass surface. You can choose. Illustratively, the arcuate member material is a hardened steel roller, steel roller, urethane roller, polyether ether ketone (PEEK) roller, shore hardness 80 urethane roller, polycarbonate (PC) roller (eg, Lexan ™). , High density polyethylene (HDPE) rollers, shore hardness 90 urethane rollers, urethane coated rollers and the like can be included. Exemplary urethane rollers can also be used to reduce rotational noise that may interfere with any signal used by the system, feedback or otherwise. Further, urethane rollers or urethane coated rollers can be used to contain foreign matter in the roller path and to prevent the stress profile in the y direction from having inward stress concentration. In embodiments used to measure the edge strength of panels and laminated structures, less compliant rollers (eg, PC, HDPE, etc.) are required to obtain adequate edge strength test results. There was found.

The exemplary dimensions of each arcuate member or roller can be varied depending on the particular embodiment of the subject matter of this application. For example, the range of the dimensions of the roller can be an outer diameter (OD) of 5 mm to 15 mm, 7 mm to 12 mm, and 9 mm to 10 mm. In some embodiments, the dimensions of the exemplary roller can be about 9 mm OD, so stress is almost entirely on the corners of the glass sheet, which is an important area where many customer complaints occur. Can be added. An exemplary system can also traverse the glass edge at speeds in the range of 50 mm / sec to 500 mm / sec or higher, or 200 mm / sec to 400 mm / sec or higher. The exemplary system has no limitation on the thickness of the glass, and thus has a thickness of less than 0.1 mm (eg, up to about 0.01 mm) to greater than 5 mm, 0.1 mm to 3 mm, 0.4 mm to 2 mm. It can be used for glass having a thickness of 0.5 mm to 1 mm and 0.5 mm to 0.7 mm.

In some embodiments, a fast closed loop stress control mechanism is used to detect cracks and ensure that the applied stress is within a predetermined value of the target, eg, within 2 MPa of the target. Can be done. For example, one arcuate member 218 can be used to load a load on the glass sheet 204, which can transmit a load cell signal to a high speed controller (not shown) that continuously monitors cracks. can. This load cell signal can also be used to control the load applied across the edge at a given speed (eg, 100 mm / sec to 500 mm / sec or higher).

Examples and Implementations Conventional inspection methods mobilize more than 100 full-time employees who are only engaged in V4PTB measurements of glass edge samples. Even with such a large amount of human resources, only a small part of the total production can be tested. This leads to quality degradation in the form of defective products being delivered to customers due to the infrequent testing. Also, since almost all resources allocated are devoted to follow-up to quality requirements, there is little or no opportunity to consider process optimization that helps improve product quality. Therefore, with the conventional method, the quality of the product may be deteriorated, but even if a defective product is manufactured, it is not possible to stop the shipment of the product before shipping or to find out how to fix the defect. It causes a dangerous situation. In contrast, in an exemplary embodiment, a significant reduction in the time spent on edge quality control, a significant increase in the amount of glass tested relative to the amount of glass produced, the edge site being tested. It allows for significant increases in proportions and real-time process feedback used for the quest for quality improvement.

Of course, the scope of claims should not be limited to the inspection of edge features alone, as it is assumed that the embodiments can also inspect surface properties. For example, embodiments of the subject matter of this application can also be incorporated into some features on the surface of the glass sheet, such as particle contamination and / or visible type surface defects such as holes, chips or scratches. However, in such embodiments, rather than providing an intensity distribution, such embodiments will utilize the size, shape and / or depth distribution of surface defects, i.e., dimensional indicators. An exemplary and non-limiting surface feature is either the size, shape or depth of the surface proximity region (eg, inside from the edge to about 20 mm), the interface region (where the surface touches the edge) and the surface defect. Including the features of. Such dimensional indicators can be used alone or in conjunction with intensity indicators obtained from edge features.

In some embodiments, the test length can span the entire length of the edge of the glass sheet or can be set to a portion of the edge of the glass sheet. Therefore, the test length can be as short as about 1 mm to 5 mm to as long as about 2600 mm, 3000 mm, 4000 mm or more, depending on the length of the glass edge.

Graded qualities can be set for each glass sheet and / or each lot, depending on the edge strength measured and tested. Additional experiments were performed to collect edge strength measurements for various glass sheets and panels or laminated structures. Embodiments of exemplary devices and methods can be used to measure edge strength from 100 MPa to 200 MPa and in any partial range within them. Further, for tempered glass (for example, chemically strengthened (ion exchange), acid etching treatment, etc.), the edge exceeds 200 MPa (for example, 200 MPa to 350 MPa, 200 MPa to 300 MPa, and any partial range thereof). It was also confirmed that the strength could be measured.

Edge strength test based on three-point bending FIGS. 6 to 9B, FIGS. 11A to 11C, and FIGS. 13A to 13D show a schematic diagram of an apparatus 200 for an edge strength test using three-point bending. A vertical load is applied to the edge of the thin sheet 204 by two supports 220 that hold it in place. In failure mode, the load is applied until the sample sheet 204 is destroyed and the peak load is recorded. This peak load is mapped to stress based on a calibration curve empirically created in advance from the strain measurement. In addition, this technique provides strain / stress along two directions (x-axis and y-axis), thus providing a significant improvement over existing methods that use only strain along the bending direction.

Digital image correlation method The digital image correlation (DIC) method uses point tracking. The DIC method is a full-field optical technique that obtains the amount of displacement and the resulting distortion. The glass sample 204 is covered with a fine black and white dot pattern 230 so that stereo cameras 222a, 222b and / or 224a / 224b with appropriate lenses capture the speckle dot pattern 230 during the test. Used for. By comparing the images at each time interval (during increasing load, or before and during loading), the movement of the dot-shaped pattern 230 can be tracked. As a result, a displacement map is provided, and distortion is obtained by differentiating. This three-dimensional (stereo) DIC method can be used to acquire a three-dimensional strain field. Bending stress can be determined based on two in-plane strain fields and equation (1):

In the equation, E is the elastic modulus, ε _xx is the strain along the bending direction (x), ε _yy is the strain along the other principal axis direction (y) in the plane, and ν is the Poisson's ratio. Existing stress conversion methods ignore the biaxiality of stress states and use Hooke's law for uniaxial stress states. This reduces the amount of information and simplifies the results as compared to the DIC techniques described herein.

In current applications, existing acrylic paints are used to form a very thin (several micrometer) coating pattern pattern 230 on glass. Since the elastic modulus of the paint is at least an order of magnitude smaller than that of the sheet 204 and its thickness is several orders of magnitude smaller than that of the sheet 204, the influence of the pattern on the measurement can be ignored.

Static mode: Edge strength tester including real-time stress measurement Ultra-thin monolithic or laminated glass (eg, material sheet) by combining edge strength testing techniques based on 3-point bending and DIC optical methods with appropriate design changes. It is possible to measure stress in real time while performing edge strength tests.

Any form of optical measurement, including the DIC method, requires an unobstructed direct optical path to the region of interest (RoI) (transformation region 208) for the measurement. Existing systems (eg, US Patent Application Publication No. 2018/0073967) do not perform direct stress measurements, and their design structure does not allow the setting of unobstructed optical paths because the rollers block the optical path. rice field. Such problems are solved using the devices described herein, such as FIGS. 6-9B, 11A-11C, and 13A-13D. Such changes and the resulting improvements are also realized when the device is run in dynamic mode. The main design items are as follows:
-Changed the upper roller from a circular wheel to a partial roller. That is, the width of the partial roller was minimized in order to maximize the optical path while maintaining the contact area with the glass sheet 204 required by the circular roller (FIG. 7, reference numerals 220a, 220b).
• Incorporate precise micrometer level adjustments into the x, y, z axis controls to allow accurate alignment of the glass and the roller / upper partial roller for studying the effect of contact. (Fig. 7, reference code 232).
• Incorporated precise micrometer level adjustments into the axis control to allow accurate alignment of the glass and rollers / partial rollers at the top to study the effects of skew (Figure 7, Reference numeral 234).
-One of the fixtures and all of the partial rollers were fixed with dowel pins for accurate alignment at the start of the test (FIG. 7, reference numerals 236a, 236b).

An optical system has been designed to perform real-time direct stress measurements using DIC technology, using an unobstructed optical path to the currently available region of interest (208). Two commercially available 4-megapixel monochrome cameras equipped with a special lens system were used to observe a 7 mm × 7 mm area 208 near the edges. The sample was covered with a random black-and-white dot pattern 230 such that the dots were about 5-7 pixels in size and the film thickness did not exceed a few micrometers. A stereo camera system was used to record a series of images (150-200 pairs of images at 4 frames per second) during the edge test experiment. After correlating this series of images to obtain a strain field, the stress was calculated using the mathematical formula (1). FIG. 10C shows an example of the history of the stress field obtained in the process of applying a load of 6N and the maximum stress during the test. It is convinced that this kind of stress visualization / measurement has never been done before. This result is correlated with a numerical simulation (eg, finite element analysis) and good agreement is seen, as shown in FIG. 10C.

Dynamic Mode: Edge Strength Tester Containing Algorithms for Real-Time Stress Measurements One embodiment of this system is manufactured with a dynamic mode and with continuous edge testing, apart from being a calibration unit in static conditions. It can also be used in an environment (or any other environment). As described and relied upon throughout this specification, an unobstructed direct optical path to the surface of the material under test facilitates more accurate direct strain measurements.

The ability to make measurements in dynamic mode is a design improvement of existing edge measurement techniques, adding the ability to directly measure stress in real time. In some embodiments, the aforementioned design is modified to continuously feed partial rollers (eg, arcuate members) as shown in FIGS. 11A-11C and 13A-13D. It may be replaced with three fully functional rollers that can capture the sample. In such a system, the rollers are placed in a position where the incoming glass edge is continuously exposed to the required bending / load. In such a system, the roller spacing and roller diameter are controlled so that there is an unobstructed optical path for inspection by the camera.

FIG. 10D illustrates how to achieve real-time stress measurements in the setting of such dynamic type edge strength tests. The edge strength tester should pre-inspect the edges prior to testing so that existing fractures are detected (sample passes through the rollers with no load / no bending). If no rupture is detected here, the system may be malfunctioning or overestimating the edge strength. During such a test, the camera can capture a series of images along the length of the edge, as shown in FIG. 11B. Then, when a load is applied to the edge of the sample on the second pass, the camera corresponds exactly to the position of the edge in the series of images taken on the first pass, as shown in FIG. 11C. As described above, by taking another series of images at the same position and correlating the corresponding images at the same position in pairs, that is, by correlating the images of the same number shown in FIGS. 11B and 11C. , Strain field and stress can be determined.

Alternatively, a device with two sets of optical systems can be used to make dynamic measurements in a single pass. An example of such a device is shown at the left end of the schematic diagram of FIG. 11C. Such a system includes a first optical system 222a, 222b, a second optical system 224a, 224b, a processor 214 connected to the first and second optical systems, and a display 228 showing the results.

What is clear as a challenge is whether it is possible to obtain strains from zero stress to peak stress states without intermediate images (150-200 pairs of images in the static test) by algorithm and image correlation. 12A and 12B show the results obtained from the proof test of this concept and confirm that accurate results can be obtained without intermediate images. As shown in FIG. 12A, a series of 150-200 pairs of images during the static test are correlated to obtain the stress distribution under a load of 11N, where FIG. 12B is the first image without an intermediate image. The stress distribution obtained by correlating the 200th image with the image is shown. These are the same and do not affect the results without the intermediate image. Thus, such embodiments describe a dynamic system in which edge strength measurements of ultrathin monolithic and laminated glass samples are performed with real-time stress visualization.

Calibration of the optical system (camera) As shown in FIGS. 13A-13D, the calibration is completed before the actual test is performed on the glass panel. By performing this operation, the image correlation software can recognize the angle and distance at which the camera is placed with respect to the test sample. This helps to transform the movement of the dot-like pattern with respect to the image pixel into a physical dimension in three-dimensional space. This calibration step is schematically illustrated with reference to FIGS. 13A-13D. FIG. 13A shows the relative positions of the cameras (222a, 222b), rollers and test panels. The upper roller is away from the panel as the test has not yet started. The test panel is then switched to a predetermined pattern printed on a flat surface (known as image correlation software). The camera takes a series of photographs of a predetermined pattern that is swiveled in three-dimensional space within the focal area of the camera, as shown in FIGS. 13B-13D. By creating a calibration file using a series of images and appropriate software, the calibration file can be used during the actual test on the panel to capture the distortion.

Ability to set static test The static mode has the following design features and acts as a calibration device (or benchmark device) for studying panel / laminated sheet design as well as other parameters. Useful for.
a) Compatible rollers (roller material and diameter)
b) Ability to change the feed angle. This helps to deal with edge testing of non-rectangular display panels.
c) Adjust the roller assembly near or far from the test edge. This makes it possible to inspect specific areas of the edge and test smaller panels (portable devices).
d) The roller can be replaced with a partial roller shape, which increases the visible area, especially near the contact point, and allows the stress distribution within that region to be examined without additional stress from the roller.

It incorporates positioning techniques such as alignment pins 236a and 236b that align various components in the correct position, which is very important for accurate inspection.

Another method of speckle coating and the method of implementing its dynamic DIC method The method of applying visible speckle dots to a test panel makes the panel unusable for commercial use. To avoid this, invisible speckles (eg, ultraviolet light, infrared light, or another invisible region of the electromagnetic spectrum) that can only be sensed by the specialized optical system installed in the device can be used. Alternatively, a laser may be used to project dots onto the panel and the speckle may be tracked by the camera during the test. The dot-shaped pattern may be random.

An exemplary embodiment describes a method of continuously measuring the fracture strength of a glass edge by applying stress only to the edge, where the stress at a site away from the edge is greater than the fracture strength at each position. It will be significantly lower. Further, using an exemplary embodiment, both sides of the edge can be subjected to substantially the same tensile stress during the measurement. Although one method for providing this continuous stress (eg, opposed and offset rollers) is described in detail, the claims that accompany this specification are acoustic. Energy and / or infrared energy (both coherent and incoherent) are also expected to be used for the same purpose of inducing stress on the edges of the glass sheet and should not be so limited. For example, focused ultrasound can be used to induce stress on the glass edge, and the devices and methods disclosed herein can be used to obtain measurements at the glass edge. In addition, IR irradiation using a laser or other means (spectrum that individual glass materials can significantly absorb) can induce stress on the glass edges, using the devices and methods disclosed herein. Therefore, the measured value at the glass edge can be obtained. Further, in the exemplary embodiment, the processing speed is at least 30 times higher, the amount of edges to be tested is at least 3 times higher, and the amount of sheet to be tested after processing is increased as compared with the conventional method. Provides continuous high-speed processing with orders of magnitude higher. Such an increase in the number of statistical samplings can ensure that the shipment of defective products to customers is reduced, and is suitable for online configurations.

The embodiments and functional operations described herein are in or one of digital electronic circuits, computer software, firmware, or hardware, including the structures disclosed herein and their structural equivalents. It can be carried out by the above combination. The embodiments described herein are of one or more computer program products, i.e., computer programs encoded in a tangible program storage medium for being executed by or controlling their operation by a data processing apparatus. It can be implemented as one or more modules of instructions. The tangible program storage medium may be a computer-readable medium. The computer-readable medium may be a machine-readable storage device, a machine-readable storage board, a memory device, or a combination thereof.

The term "processor" or "controller" refers to any device, device, and machine for processing data, including programmable processors, computers, or multiprocessors, or multicomputers as embodiments. Can include. In addition to the hardware, the processor contains the code that creates the execution environment for the target computer program, such as the processor firmware, protocol stack, database management system, operating system, or a combination of one or more of them. Can include.

Computer programs (also known as programs, software, software applications, scripts, or code) can be written in any form of a compiler or interpreter language, or any form of programming language, including declarative or procedural languages. It can be implemented as a stand-alone program suitable for use in a computer environment, or in any form, including as a module, component, subroutine, or other unit. Computer programs do not always support files in the file system. A program may be part of a file that holds other programs or data (eg, one or more scripts stored in a markup language document), a single file dedicated to the target program, or multiple collaborative files (eg,). , A file that stores one or more modules, subprograms, or parts of code). Computer programs can be implemented to run on one computer, or on multiple computers in one location or distributed across multiple locations and interconnected by communication networks.

The steps described herein can be performed by one or more programmable processors that execute one or more computer programs that perform functions by processing input data to produce output. This process and logic flow can also be performed by dedicated logic circuits, for example FPGAs (Field Programmable Gate Arrays) or ASICs (Application Specific Integrated Circuits), for example, logic dedicated to the device. The circuit may be mounted.

Suitable processors for executing computer programs include, in one embodiment, both general purpose microprocessors and dedicated microprocessors, and any one or more processors of any kind of digital computer. Generally, the processor receives instructions and data from read-only memory and / or random access memory. Essential components of a computer are a processor that executes instructions and one or more data memory devices that store instructions and data. In general, computers are equipped with one or more mass storage devices for storing data, such as magnetic disks, magneto-optical disks, or optical disks, or receive data, transmit data, or both. Operatively linked to one or more mass storage devices for doing so. However, the computer does not have to have such a device. In addition, the computer can be built into another device, for example a mobile phone, a personal digital assistant (PDA), to name a few.

Computer-readable media suitable for storing computer program instructions and data include all forms of data memory, including non-volatile memory, media and memory devices, and in embodiments include semiconductor memory devices (eg, EPROM, EEPROM). , And flash memory devices), magnetic disks (eg, internal hard disks or removable disks), optomagnetic disks, CD-ROM disks, DVD-ROM disks, and the like. Processors and memory can also be complemented or incorporated with dedicated logic circuits.

To provide user interaction, as shown in the drawings included herein, the embodiments described herein are display devices for displaying information to the user, such as a CRT. Performed on a computer having a (catalyst tube) or LCD (liquid crystal display) monitor, etc., and a keyboard and pointing device that allows the user to input to the computer, such as a mouse or trackball, or a touch screen. Can be done. Other types of devices may also be used to provide dialogue with the user, and in embodiments, input from the user is received in any form, including acoustic input, voice input, or contact input. be able to.

The embodiments described herein are back-end components (eg, data servers), middleware components (eg, application servers), or front-end components (eg, users interacting with each other about the implementation of the subject matter described herein). In a computing system that includes (a client computer with a graphical user interface or web browser that allows you to), or includes any combination of one or more of such back-end components, middleware components, or front-end components. Can be carried out. The components of this system can be interconnected by any form or medium of digital data communication, such as a communication network. Embodiments of communication networks include local area networks (“LAN”) and wide area networks (“WAN”), such as the Internet.

The computing system can include clients and servers. Clients and servers are generally remote from each other and typically interact over a communication network. The client-server relationship arises when a computer program runs on each computer and establishes a client-server relationship with each other.

It will be appreciated that the various embodiments disclosed may involve certain features, elements or steps described in connection with the particular embodiment. It is also understood that a particular feature, element or process may be described in connection with a particular embodiment but may be exchanged for or combined with another embodiment by various combinations or substitutions not shown. Will be.

Also, as used herein, the terms "the", "a" or "an" mean "at least one" and unless expressly indicated that there is only one, "one". It should be understood that it should not be limited to the meaning of "only". Thus, for example, reference to "one component" includes having more than one such component, unless the context explicitly states that there is only one component.

As used herein, the range is expressed as a range from one particular value labeled "about" and / or to another particular value labeled "about". There is. When the range is so represented, the exemplary values include from one particular value and / or to another particular value. Similarly, if a particular value is expressed as an approximation using the antecedent "about", it can be seen that the particular value forms another aspect. Moreover, it can be seen that the endpoints of each of these ranges are significant, both in relation to the other endpoint and independent of the other endpoint.

As used herein, "substantial," "substantially," and variations thereof, that the described features are equal to, or substantially equal to, certain values or descriptions. Note. Further, "substantially similar" means that the two values are equal or substantially equal. In some embodiments, "substantially similar" may refer to values within about 10% of each other, eg, about 5% of each other, or about 2% of each other.

Unless otherwise stated, the methods described herein are not intended to be construed as having to be performed in a particular order. Therefore, if the claims relating to the method do not actually describe the order in which the steps should follow, or the claims or specification that the steps should be limited to a particular order. Unless otherwise stated in, there is no intention to suggest a particular order.

Various features, elements or steps in a particular embodiment may be disclosed using the transition phrase "comprising", which transition clause is "consisting" or "substantially from". It should be understood that alternative embodiments that can be explained using the transitional phrase "consisting essentially of" are suggested. Thus, for example, alternative embodiments suggested for an apparatus comprising A + B + C include an embodiment in which the apparatus comprises A + B + C and an embodiment in which the apparatus substantially comprises A + B + C.

It will be apparent to those skilled in the art that various modifications and changes can be made to the embodiments of the present disclosure without departing from the spirit and scope of the present disclosure. Modifications, combinations, partial combinations and variations of the disclosed embodiments incorporating the spirit and scope of the present disclosure may be recalled by those skilled in the art, and thus the present disclosure is ancillary claims and their equivalents. It should be interpreted as including everything that falls within the scope of.

Hereinafter, preferred embodiments of the present invention will be described in terms of terms.

Embodiment 1
A device for testing material sheets,
Multiple assemblies that load the area of the material sheet,
A detection mechanism that directly acquires the measured value under no load on the surface of the region and the measured value under load on the surface of the region while the load is applied to the region.
A device for testing a material sheet, comprising a processor that analyzes the unloaded and loaded measurements to determine the stresses caused by the loaded load.

Embodiment 2
The plurality of assemblies contact a first assembly that includes an arcuate member for contacting the first side surface of the sheet and a second side surface of the sheet opposite to the first side surface. The apparatus according to embodiment 1, comprising a second assembly comprising two arcuate members spaced apart from each other.

Embodiment 3
The apparatus according to the second embodiment, wherein the one arcuate member is arranged along the longitudinal direction between the two arcuate members arranged apart from each other.

Embodiment 4
The detection mechanism comprises a first optical system that is disposed facing the second side surface of the sheet and detects the surface between two arcuate members spaced apart from each other. 3. The device according to 3.

Embodiment 5
The apparatus according to embodiment 4, wherein the first optical system acquires the measured value under no load and the measured value under load.

Embodiment 6
The device according to embodiment 5, wherein in the static mode, the load of the load is increased until a predetermined load is reached or the sheet is detected to be broken.

Embodiment 7
The detection mechanism faces the second side surface of the sheet to measure an unloaded measurement before the sheet advances between the two mutually spaced arcuate members. The apparatus according to embodiment 4, wherein the first optical system detects the surface in order to measure the measured value under the load.

8th embodiment
The device comprises a dynamic mode in which the sheet passes through the plurality of assemblies twice.
The unloaded measurements are acquired in one pass when no load is applied, and the loaded measurements are acquired in another pass when a load is applied. The device according to the fifth embodiment.

Embodiment 9
The device according to embodiment 1, wherein the arcuate member is selected from the group consisting of a cylindrical roller, a belt roller, and a bearing roller.

Embodiment 10
The plurality of assemblies are configured such that the sheet advances through the plurality of assemblies.
9. The apparatus of embodiment 9, wherein a plurality of stress measurements are determined continuously or intermittently along the edges of the sheet passing through the plurality of assemblies.

Embodiment 11
The device according to embodiment 1, wherein the stress is determined in at least two dimensions.

Embodiment 12
The apparatus according to embodiment 1, wherein the pattern on the surface of the region facilitates measurement of the measured value under no load and the measured value under load.

Embodiment 13
The apparatus according to embodiment 1, further comprising a display configured to display the stress result.

Embodiment 14
A method of testing material sheets
The process of providing the material sheet and
The step of acquiring the measured value at no load on the surface of the region of the material sheet, and
The process of applying a load to the region of the material sheet and
A step of acquiring a measured value under a load on the surface of the region of the material sheet, and
A method of testing a material sheet comprising the step of determining the stress generated by the load of the load based on the measured values under no load and the measured values under load.

Embodiment 15
13. The method of embodiment 14, wherein the load of the load deforms the surface of the region of the material sheet.

Embodiment 16
13. The method of embodiment 14, wherein in static mode, the first optical system obtains the unloaded and loaded measurements.

Embodiment 17
The method according to embodiment 14, wherein in the static mode, the load of the load is increased until a predetermined load is reached or the sheet is detected to be broken.

Embodiment 18
The first optical system acquires the measured values under the load, and the second optical system acquires the measured values under the no load.
The method according to embodiment 14, wherein the measured value under no load is acquired before the measured value under load.

Embodiment 19
In the dynamic mode, the sheet is longitudinally advanced through the test device to sequentially obtain the unloaded and loaded measurements on the surface of the region, and then the said. 18. The method of embodiment 18, which is compared in the determination step.

20th embodiment
13. The method of embodiment 14, wherein the stress is determined in at least two dimensions.

21st embodiment
13. The method of embodiment 14, wherein the pattern on the surface of the region facilitates measurement of the unloaded and loaded measured values.

204 Material Sheets 206a, 206b Multiple Assemblies 206a First Assembly 206b Second Assembly 208 Region 212 Surface 214 Processor 218 One Arc Member 220a, 220b Two Arc Members 222 First Optical System 224a, 224b Second Optical system 228 display 230 pattern pattern

Claims (13)

A device for testing material sheets,
Multiple assemblies that load the area of the material sheet,
A detection mechanism that directly acquires the measured value under no load on the surface of the region and the measured value under load on the surface of the region while the load is applied to the region.
A device for testing a material sheet, comprising a processor that analyzes the unloaded and loaded measurements to determine the stresses caused by the loaded load. The plurality of assemblies contact a first assembly that includes an arcuate member for contacting the first side surface of the sheet and a second side surface of the sheet opposite to the first side surface. The device of claim 1, comprising a second assembly comprising two arcuate members spaced apart from each other. The device according to claim 2, wherein the one arcuate member is arranged along the longitudinal direction between the two arcuate members arranged apart from each other. The detection mechanism comprises a first optical system that is disposed opposite to the second side surface of the sheet and detects the surface between two arcuate members spaced apart from each other. 3. The device according to 3. The device according to claim 4, wherein the first optical system acquires the measured value under no load and the measured value under load. The device according to claim 5, wherein in the static mode, the load of the load is increased until a predetermined load is reached or the fracture of the sheet is detected. The detection mechanism faces the second side surface of the sheet to measure an unloaded measurement before the sheet advances between the two mutually spaced arcuate members. The apparatus according to claim 4, wherein the first optical system detects the surface in order to measure the measured value under the load. The device comprises a dynamic mode in which the sheet passes through the plurality of assemblies twice.
The unloaded measurements are obtained in one pass when no load is applied, and the loaded measurements are obtained in another pass when the load is loaded. Item 5. The apparatus according to Item 5. The device according to claim 1, wherein the arcuate member is selected from the group consisting of a cylindrical roller, a belt roller, and a bearing roller. The plurality of assemblies are configured such that the sheet advances through the plurality of assemblies.
9. The apparatus of claim 9, wherein a plurality of stress measurements are determined continuously or intermittently along the edges of the sheet passing through the plurality of assemblies. The device of claim 1, wherein the stress is determined in at least two dimensions. The apparatus according to claim 1, wherein the pattern on the surface of the region facilitates measurement of the measured value under no load and the measured value under load. The apparatus of claim 1, further comprising a display configured to display the stress result.

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