CLAIM OF PRIORITY

[0001] This application claims the benefit of priority under 35 U.S.C. § 119 of U. S. Provisional Application No. 63/284,099, filed on November 30, 2021, the contents of which are relied upon and incorporated hereinby reference in their entirety.

Background

Field

[0002] The present specification generally relates to localized polishing fixtures and processes of using the same.

Technical Background

[0003] Localized polishing and patterning on a glass surface can be costly and time consuming because conventional polishing cannot provide the level of accuracy needed. A computer numerical control (CNC) milling machine is an attractive option for controlling the XY movement of a polishing tool. However, most CNC machines operate in a distance-control machine, such as by controlling tool distance in the Z direction. Polishing is a pressure dependent process, rendering existing distance-control CNC machines unsuitable for localized polishing applications.

[0004] Accordingly, a need exists for fixtures and methods to convert a distance-control CNC machine to a pressure-control system for use in localized polishing applications.

SUMMARY

[0005] According to an aspect (1), a fixture is provided. The fixture comprises: a base, wherein a major surface of the base defines an xy-plane, and a z-axis extends orthogonal to the xy-plane; a stage; a workpiece chuck mounted to the stage, wherein the workpiece chuck is configured to secure a workpiece; an alignment feature mounted to the base and configured to prevent the rotation of the stage around the z-axis; a spring, wherein the spring is located between the stage and the base, and transfers forces appliedto the stage to the base; and a spring alignment element configured to maintain the axis of the spring parallel to the z-axis. [0006] According to aspect (2), the fixture of aspect (1) is provided, wherein the spring alignment element comprises a shaft mounted to the stage and a sleeve mounted to the base, the shaft extends into an inner cavity of the sleeve, the spring is mounted on the shaft and bears against the stage and the sleeve, and the shaft, sleeve, and spring are coaxial.

[0007] According to aspect (3), the fixture of aspect (2) is provided, wherein the shaft is movably engaged with the sleeve to limit movement of the stage to the direction of the z-axis.

[0008] According to aspect (4), the fixture of any of aspect (2) to the preceding aspect is provided, wherein the sleeve comprises a collar configured to engage an end of the spring.

[0009] According to aspect (5), the fixture of any of aspect (1) to the preceding aspect is provided, wherein the alignment feature comprises a rail aligned parallel to the z-axis and a carriage configured to engage the rail and allow movement of the stage in the direction of the z-axis.

[0010] According to aspect (6), the fixture of aspect (5) is provided, wherein the carriage is mounted to the stage.

[0011] According to aspect (7), the fixture of any of aspect (5) to the preceding aspect is provided, comprising a second alignment feature, the second alignment feature comprising a second rail aligned parallel to the z-axis and a second carriage configured to engage the second rail and allow movement of the stage in the direction of the z-axis.

[0012] According to aspect (8), the fixture of any of aspect (1) to the preceding aspect is provided, wherein the spring alignment element comprises a cylinder mounted to the base and the spring is located in an inner cavity of the cylinder.

[0013] According to aspect (9), the fixture of any of aspect (1) to the preceding aspect is provided, wherein the alignment feature prevents the movement of the stage in in directions other than parallel to the z-axis.

[0014] Accordingto aspect (10), the fixture of any of aspect (l) to the preceding aspect is provided, wherein the workpiece chuck is removably mounted to the stage.

[0015] Accordingto aspect (l 1), the fixture of any of aspect (l) to the preceding aspect is provided, wherein the workpiece chuck contains vacuum channels to secure the workpiece. [0016] Accordingto aspect (12), the fixture of any of aspect (1) to the preceding aspect is provided, further comprising a load cell configured to measure the load applied to the stage by the spring.

[0017] Accordingto aspect (13), the fixture of any of aspect (l) to the preceding aspect is provided, wherein the spring is a coil spring.

[0018] Accordingto aspect (14), the fixture of any of aspect (1) to aspect (12) is provided, wherein the spring is a pneumatic cylinder, the pneumatic cylinder comprising a piston rod aligned with the z-axis.

[0019] According to aspect (15), the fixture of aspect (14) is provided, wherein the pneumatic cylinder is mounted to the base utilizing a mounting bracket.

[0020] Accordingto aspect (16), the fixture of any of aspect (1) to the preceding aspect is provided, comprising a locking system that selectively locks the stage to the base and prevents the movement of the stage in the direction parallel to the z-axis relative to the base.

[0021] Accordingto aspect (17), a method is provided. The method comprises: moving a rotary polishing tool along a z-axis to apply a force to a workpiece secured in a workpiece chuck; determining the force applied to the workpiece by the rotary polishing tool with a load cell; and moving the rotary polishing tool along the z-axis to maintain the pressure applied to the workpiece by the rotary polishing tool in the range greater than or equal to 1 psi to less than or equal to 15 psi, wherein: the workpiece chuck is mounted to a stage; an alignment feature is mounted to a base and configured to prevent the rotation of the stage around the z-axis; a major surface of the base defines an xy -plane, and the z-axis extends orthogonal to the xy -plane; a spring is located between the stage and the base, and transfers the force applied to the workpiece by the rotary polishing tool to the base; and a spring alignment element is configured to maintain the major axis of the spring parallel to the z-axis.

[0022] According to aspect (18), the method of aspect (17) is provided, comprising moving the rotary polishing tool in a direction orthogonal to the z-axis to produce a polished region on the workpiece.

[0023] According to aspect (19), the method of any of aspect (17) to the preceding aspect is provided, wherein the spring is a pneumatic cylinder. [0024] Accordingto aspect (20), the method of aspect (19) is provided, comprising adjusting the pressure of the pneumatic cylinder to adjustthe force applied to the workpiece by the rotary polishing tool.

[0025] Additional features and advantages will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the embodiments described herein, including the detailed description which follows, the claims, as well as the appended drawings.

[0026] It is to be understood that both the foregoing general description and the following detailed description describe various embodiments and are intended to provide an overview or framework for understanding the nature and character of the claimed subject matter. The accompanying drawings are included to provide a further understanding of the various embodiments and are incorporated into and constitute a part of this specification. The drawings illustrate the various embodiments described herein and, together with the description, serve to explain the principles and operations of the claimed subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] FIG. 1 is a side-view along the y-axis of a fixture according to an embodiment;

[0028] FIG. 2 is a side-view along the x-axis of the fixture of FIG. 1 ;

[0029] FIG. 3 is a cross-sectional view along the x-axis of FIG. 1;

[0030] FIG. 4 is a side-view along the y-axis of a fixture accordingto an embodiment;

[0031] FIG. 5 is a cross-sectional view along the y-axis of FIG. 4;

[0032] FIG. 6 is a cross-sectional view along the y-axis of a fixture according to an embodiment;

[0033] FIG. 7 is a top-down view of a fixture accordingto an embodiment;

[0034] FIG. 8 is a plot of force as a function of spring compression for two different springs;

[0035] FIG. 9 A is a plan view of an exemplary electronic device incorporating any of the glass-based articles disclosed herein; [0036] FIG. 9B is a perspective view of the exemplary electronic device of FIG. 9 A;

[0037] FIGs. 10A and 10B are measured surface profiles for polished articles produced according to an embodiment;

[0038] FIGs. 11 A and 1 IB are measured surface profiles for polished articles produced according to a comparative process;

[0039] FIG. 12 is a plot of force as a function of time as measured by a load cell in a fixture according to an embodiment during a polishing process; and

[0040] FIG. 13 is a collection of plots characterizing the polished region of polished articles produced according an embodiment.

DETAILED DESCRIPTION

[0041] Reference will now be made in detail to fixtures for converting a distance-control CNC machine to a pressure-control system for use in localized polishing applications. Methods for operating such modified machines are also described.

[0042] In the following description, like reference characters designate like or corresponding parts throughout the several views shown in the figures. It is also understood that, unless otherwise specified, terms suchas“top,” “bottom,” “outward,” “inward,” andthelike are words of convenience and are not to be construed as limiting terms. Whenever a group is described as consisting of at least one of a group of elements or combinations thereof, it is understood that the group may consist of any number of those elements recited, either individually or in combination with each other. Unless otherwise specified, a range of values, when recited, includes both the upper and lower limits of the range as well as any ranges therebetween. As used herein, the indefinite articles “a,” “an,” and the corresponding definite article “the” mean “atleast one” or “one or more,” unless otherwise specified. It also is understood thatthe various features disclosedin the specification and the drawings can be used in any and all combinations.

[0043] All ranges disclosed in this specification include any and all ranges and subranges encompassed by the broadly disclosed ranges whether or not explicitly stated before or after a range is disclosed.

[0044] It is noted that the terms "substantially" and "about" may be utilized herein to represent the inherent degree of uncertainty that may be attributed to any quantitative comparison, value, measurement, or other representation. These terms are also utilized herein to represent the degree by which a quantitative representation may vary from a stated reference without resulting in a change in the basic function of the subject matter at issue. As utilized herein, when the term “about” is used to modify a value, the exact value is also disclosed.

[0045] The fixtures described herein support a workpiece, such as a glass or glass-ceramic workpiece, thatrequires shallow patterning or spot polishing. The fixturehelps create auniform polished region by creating constant force application during spot polishing, even when utilizing a CNC machine.

[0046] Utilizing a CNC machine in a localized polishing process can provide multiple benefits. Such machines are often utilized in glass processing, for purposes such as finishing cut edges of the glass or drill holes in the glass. As a result, utilizing a CNC machine to polish a portion of a glass-based substrate may not require the purchase of additional manufacturing equipment. However, polishing processes are primarily pressure-controlled while CNC machines typically operate in a distance-control regime. A CNC process generally provides the advantage of being a fast process, requiring limited cleaning of the processed part, and providing a near-net shape finish. Polishing processes provide optimized surface quality. A modified CNC machine of the type described herein combines the benefits of a CNC machine and a polishing process.

[0047] The fixtures described herein are a more robust solution than approaches to converting a distance-control CNC machine to a pressure-control CNC machine, such as floating a rotating polishing tool on a pressure system including a spring. Using a pressure system on the rotating polishing tool limits the CNC machine capability by limiting machine rotational speed (rpm), CNC machine dimensions, and polishing tool geometries. A floating rotating polishing tool also introduces errors in the alignment of the rotating polishing tool axis with the axis of the spindle of the CNC machine and reducesthe reliability of the CNC machine.

[0048] The fixtures described herein provide a multitude of benefits. The pressure-control fixtures provide significantly higher polishing accuracy compared to distance-control CNC machines, and require less set up time and probing. The pres sure -control fixtures allow the usage of CNC machines with a lower degree of z-direction accuracy to achieve the same polishing results, reducing cost and increasing machine availability. The fixtures are capable of producing a polished area with a high degree of uniformity, such as a polished region with a 6 mm diameter, a 2 pm depth, and a peak-to-valley of about 300 nm. The CNC machine may operate at higher rotational speed than when a rotational polishing tool is floated on a spring pressure system. The use of a spring as the force control in the fixtures allow the polishing pressure to be controlled by adjusting the z-height of the rotary polishing tool. The improved polishing pressure control provided by the fixtures produce more repeatable polishing results, increasing process yields. As described herein, the fixtures may include a load cell to allow the polishing pressure to be monitored during the process and adjusted in real time, unlike other polishing methods. The spring in the fixtures may be a pneumatic system, increasing accuracy and adjustability with minimum cost. In comparison, utilizing a pneumatic system in the spindle to provide pressure control is challenging and costly. The fixtures may be used on a wide range of workpiece sizes, governed primarily by the maximum allowable size of the CNC machine. The fixtures can be locked in translation and rotation about all axes to allow the CNC machine to be used in a non-modified manner without removing the fixture.

[0049] The fixtures described herein allow a rotary polishing tool to be directly attached to the spindle of the CNC milling machine, avoiding the issues associated with a floating rotational polishing tool. The pressure control is provided by a spring included in the fixture.

[0050] An exemplary fixture is shown in FIGS. 1-3. The fixture includes a base 110 that defines an xy -plane, with the z-axis extending orthogonally to the xy -plane definedby the base. The base may be mounted to the xy stage of a CNC machine by any appropriate mounting means, such as with threaded fasteners. A stage 120 supports a workpiece chuck 190 configured to secure a workpiece 600. At least one alignment feature 130 is mounted to the base 110 and configured to prevent rotation of the stage 120 around the z-axis. A spring 140 is located between the stage 120 and the base 110, such that the spring 140 transfers forces applied to the stage 120 to the base 110. The spring alignment element 150 is configured to maintain the axis of the spring 140 parallel to the z-axis.

[0051] The spring alignment element 150 may include a shaft 152 and a sleeve 154. The shaft 152 is mounted to the stage 120 and the sleeve 154 is mounted to the base. The shaft 152 extends into an inner cavity 155 of the sleeve 154. The spring 140 is mounted on the shaft 152 and bears againstthe stage 120 and the sleeve 154. The spring 140, the shaft 152, andthe sleeve 154 are coaxial. The spring 140 may be a coil spring. The shaft 152 is movably engaged with the sleeve 154 in a manner that limits the movement of the stage 120 to the direction of the z- axis. The tolerance and engagement length between the shaft 152 and the sleeve 154 combine to prevent linear motion and rotation of the stage 120 about the x- and y-axis. The shaft 152 may be press fit to the stage 120. The sleeve 154 may be press fitto the base 110. The sleeve may include a collar 157 configured to engage an end of the spring 120. The collar 157 may be located at the end of the sleeve 154 or along the body of the sleeve.

[0052] The spring 140 selected for use in the fixture may have any appropriate strength. Utilizing a spring with a high spring strength increases the process speed, but a spring strength that is too high may damage the workpiece surface or the rotary polishing tool. In a preferred embodiment, the spring may have a strength greater than or equal to 50 gr/mm to less than or equal to 300 gr/mm. The force F applied to the workpiece by the compression of the spring when the rotary polishing tool moves in the z-direction is give by the formula F=k z, where k is the spring constant of the spring andzis the amountof springcompression. This relation ship allows the force applied to the workpiece to be predictably changed by moving the rotary polishing tool in the z-direction. By way of example, FIG. 8 shows a plot of spring force as a function of compression for two exemplary coil springs. The polishing processes described herein are conducted in the plateau region of the spring performance curves in FIG. 8, allowing for predictable and repeatable changes applied force with changes in z-position of the rotary polishing tool.

[0053] The fixture 100 may include more than one alignment feature 130. In embodiments, the fixture 100 includes at least two alignment features, such as two alignment features or four alignment features. In a preferred embodiment, the fixture includes a rectangular or square stage 120 and four alignment features 120, where an alignment feature 120 is located at each edge of the stage 120. In embodiments, the alignment feature 130 may be a simple bracket, such as an L-shaped bracket. The alignment feature 130 and the base 110 may be separate components, such that the alignment feature 130 is removably mounted to the base 110. Alternatively, the base 110 and the alignment feature 130may be formed as a single component or joined to form a single component. The alignment feature 130 prevents the movement of the stage 120 in directions other than parallel to the z-axis.

[0054] The stage 120 and the workpiece chuck 120 may be separate components, such that the workpiece chuck 120 is removably mounted to the stage. Alternatively, the stage 120 and the workpiece chuck 190 may be formed as a single component or joined to form a single component. The workpiece chuck 190 may include vacuum channels 194 to secure the workpiece 600. A vacuum port 192 is provided in the stage 120 or the workpiece chuck 190 for connection to an external vacuum source, and is configuredto supply vacuumto the vacuum channels 194 in the workpiece chuck 190.

[0055] A fixture 100 including an alternative alignment feature 130 is shown in FIGs. 4 and 5. The alignment feature 130 includes a rail 132 aligned parallel to the z-axis and a carriage 136 configured to engage the rail 132 and allow movement of the stage 120 in the direction of the z-axis. Stated differently, the rail 132 and carriage 136 interact to prevent movement of the stage in directions other than the z-direction. The rail 132 may be mounted to a rail mount bracket 134, which in turn may be mounted to the base 110. The carriage 136 may be mounted to a carriage mount bracket 138, which in turn maybe mounted to the stage 120. Alternatively, rail mount bracket 134 may be mounted to the stage 120 and the carriage mount bracket 138 may be mounted to the base 110. The rail 132 and the rail mountbracket 134 may be removably joined together or may be formed as a single component. The carriage 136 and the carriage mountbracket 138 may be removably j oined together or may be formed as a single component. As shown in FIGs. 4 and 5, the fixture 100 may include two alignment features 130 including a rail 132 and carriage 136 configuration. In embodiments, the fixture 100 may include four alignment features 130 including a rail 132 and carriage 136 configuration.

[0056] The fixture 100 shown in FIGs. 4 and 5 also includes an alterative spring alignment element 250. The spring alignment element 250 includes a cylinder 252 mounted to the base 110. The cylinder 252 may be mounted to the base 110 by a mounting block 256. The spring 140 is disposed within an inner cavity 255 of the cylinder 252. The inner cavity 255 of the cylinder 252 is configured to constrain the movement of the spring 140 in the x- and y- directions but allows the spring to move in the z-direction. The cylinder 252 and the spring 140 are coaxial. An end of the spring 140 bears against the stage 120, and may be in contact with a load cell 124 thatis mounted to the stage 120. The load cell 124 may be mounted to the stage 120 by a load cell mounting bracket 122. The load cell 124 is configured to measure the load applied to the stage 120 by the spring 140. A second end of the spring 140 may bear against the mounting block 256, against the base 110, or against a collar in the cylinder 252. As shown intFIGs. 4 and 5, the spring 140 is a coil spring. The mountingblock256 and the cylinder 252 may be removably joined together or may be formed as a single component. The mounting block 256 and the base 110 may be removably joined together or may be formed as a single component. [0057] The fixture 100 shown in FIG. 6 includes an alternative spring 340 and spring alignment element 350. The spring340 isapneumatic cylinderthatincludes a pneumatic piston rod 342 and an air chamber 344. The pneumatic piston rod 342 may be engaged directly with the stage 120 or may engage a load cell 124 via a load cell mounting bracket 122. In embodiments, the pneumatic piston rod 342 is threadedly engaged with the load cell mounting bracket 122. The spring 340 is mounted to a spring alignment element 350 that is mounted to the base 110. The spring alignment element 350 is configured to maintain the operating axis of the spring 340 and the pneumatic piston rod 342 parallel to the z-axis. The use of a pneumatic spring 340 allows the adjustment of the pressure in the air chamber 344 to change the spring force. This allows easy adaptation of the fixture to different springforces withoutremovingthe spring 340. In addition, it is possible to adjust the pressure in the air chamber 344 based on feedback from the load cell 124 during the polishing process, providing dynamic control of the polishing pressure. The pneumatic cylinder may also be adjusted to lock the stage 120 in the z- direction, such as by bringing the stage into contact with a hard stop, and allowing the CNC machine to operate in a standard distance-control regime.

[0058] A top-down view of the stage 120 and workpiece chuck 190 is shown in FIG. 7. The workpiece chuck 190 includes vacuum channels 1974 configured to secure a workpiece 600. The workpiece chuck 190 may be mounted to the stage 120 by any appropriate mechanism, such as with threaded fasteners. The stage 120 may include a variety of mounting holes 122, such that the stage 120 is compatible with workpiece chucks 190 of different sizes and geometries.

[0059] The fixture 100 may include a locking system. The locking system is configured to selectively lock the stage 120 relative to the base 110 to prevent movement of the stage 120 relative to the base 110. As the alignment features constrain movement in the x- and y- directions, the locking system is configured to prevent movement of the stage in the z-direction relative to the base. The locking system may be pneumatic, as described above, mechanical, or electro-mechanical in nature. The locking system allows the CNC machine to which the fixture 100 is mounted to operate in a standard distance-control regime without removing the fixture. In this manner, the locking system provides flexibility to the CNC machine and reduces the time required to switch between a pressure-control regime and a distance-control regime.

[0060] The polishing includes mechanically polishing the desired region of workpiece to remove material from the polished region and produce polished region with a thickness that is less than the thickness of the non-polished regions. The use of a computer numerical control (CNC) machine to perform the polishing process allows precise control of the polished region and a relatively quick polishing time. The polish tool may be operated on the basis of a desired pressure exerted on the workpiece. The pressure control reduces the polishing process time, minimizes the polishing tool consumption and damage, and also achieves a high level of polish control. The polishing process can produce a R _a surface roughness of less 10 nm and peak-to- valley distance of less than 100 nm and may be adjusted by selection of the polishing tool diameter, polishing tool binder medium, coolant type, polishing tool spindle speed, polishing pattern, and feedrate.

[0061] Aspects of the CNC polishing process including machine specifications, polishing tool properties and geometry, pressure-control system, coolant type, and process operation parameters (tool rotation speed, feed rate, and polishing pattern) all impact the properties of the polished article.

[0062] The polishing method may include moving a rotary polishing tool along a z-axis to apply a force to a workpiece secured by the workpiece chuck of the fixture. The force applied to the workpiece by the rotary polishing tool is then determined the load cell of the fixture, and the rotary polishing tool is moved along the z-axis to maintain the pressure applied to the workpiece by the rotary polishing tool in a predetermined range. The pressure applied to the workpiece by the rotary polishing tool may be in the range greater than or equal to 1 psi to less than or equal to 15 psi, such as greater than or equal to 2 psi to less than or equal to 14 psi, greater than or equal to 3 psi to less than or equal to 13 psi, greater than or equal to 4 psi to less than or equal to 12 psi, greater than or equal to 5 psi to less than or equal to 11 psi, greater than or equal to 6 psi to less than or equal to 10 psi, greater than or equal to 7 psi to less than or equal to 9 psi, greater than or equal to 3 psi to less than or equal to 8 psi, and any and all subranges formed between any of the foregoing endpoints. The pressure applied to the glass-based substrate may be determined when the area of the rotary polishing tool in contact with the workpiece and the force applied to by rotary polishing tool to the workpiece the z-direction is known. To control the pressure applied to the glass-based substrate, the rotary polishing tool may be moved away from the glass-based substrate when the pressure is too high and towards the glass-based substrate when the pressure is insufficient.

[0063] The pressure applied to the workpiece by the rotary polishing tool may be adjusted by changing the strength of the spring in the fixture. In embodiments, the spring is a pneumatic cylinder and the pressure applied to the workpiece is adjusted by adjusting the pressure in the pneumatic cylinder in response to data from the load cell. The adjustment of the pressure in the pneumatic cylinder may occur during the polishing process.

[0064] The polishing process includes moving the rotary polishing tool in a direction orthogonal to the z-axis to produce a polished region of the workpiece. The rotary polishing tool may be moved in any pattern appropriate to produce the desired polished region shape.

[0065] Generally, the details of the polishing process and rotary polishing tool are the same as those described in U.S. Patent App. No. 17/536,276 filed November 29, 2021 titled “Textured Glass-based Articles with Multiple Haze Levels and Processes of Producing the Same,” (the ’276 application), the contents of which are incorporated herein by reference in their entirety, with the exception that the fixtures described herein are used to convert the CNC machines to pressure-control as opposed to floating the rotary polishing tool. The polished articles produced by the processes employing the fixtures described herein may have the characteristics of those described in the ’276 application.

[0066] The polished workpieces produced by the processes disclosed herein may be incorporated into another article such as an article with a display (or display articles) (e.g., consumer electronics, including mobile phones, tablets, computers, navigation systems, and the like), architectural articles, transportation articles (e.g., automobiles, trains, aircraft, sea craft, etc.), appliance articles, orany article that requires some transparency, scratch-resistance, abrasion resistance or a combination thereof. An exemplary article incorporating any of the polished workpieces disclosed herein is shown in FIGs. 9A and 9B. Specifically, FIGs. 9A and 9B show a consumer electronic device 200 including a housing 202 having front 204, back 206, and side surfaces 208; electrical components (not shown)that are at least partially inside or entirely within the housing and including at least a controller, a memory, and a display 210 at or adj acent to the front surface of the housing; and a cover substrate 212 at or over the front surface of the housing such that it is over the display. In embodiments, at least a portion of at least one of the cover substrate 212 and/or the housing 202 may include any of the polished workpieces disclosed herein.

[0067] As described above, the polished workpieces produced by the processes described herein can be used as a front or back cover for mobile electronic devices. The polished workpieces not only serve as protective covers but also serve to enable various functionalities of the mobile electronic devices. For example, the polished workpieces may possess a polished region that enables the functioning of a camera covered by the glass-based article.

[0068] The workpieces polished by the processes disclosed herein may be formed from any appropriate material. In embodiments, the workpieces maybe glass or glass-ceramic materials, the workpieces may be transparent in the visible wavelength range. Exemplary glass-ceramic materials are those described in U.S. Patent App. Pub. No. 2016/0102010 Al, titled “High Strength Glass-Ceramics Having Petalite and Lithium Silicate Structures,” published April 14, 2016, the contents of which are incorporated herein by reference in their entirety. Exemplary glass materials include an alkali aluminosilicate glass, such as a lithium aluminosilicate glass, and those described in U.S. Patent App. Pub. No. 2019/0300422 Al, titled “Glasses Having High Fracture Toughness,” published October 3, 2019, the contents of which are incorporated herein by reference in their entirety.

EXAMPLES

[0069] Embodiments will be further clarified by the following examples. It should be understood that these examples are not limiting to the embodiments described above.

Example 1

[0070] 16 sample workpieces were polished using a fixture mounted on a CNC machine of the type described herein. The polished regions were 15 mm in diameter and had a depth of 1- 2 pm. The polished region profiles were measured in the x- and y-directions on a Zygo optical surface profiler, and are shown in FIGs. 10A and 10B.

[0071] 15 sample workpieces were polishedin the same manner as the 16 sample workpieces except that a floating rotary polishing tool was used instead of the fixture to convert the CNC machine to pressure-control to form comparative polished articles. The polishedregion profiles were measured in the x- and y-directions on a Zygo optical surface profiler, and are shown in FIGs. HA and 11B.

[0072] As shown in FIGs. 10A, 10B, 11 A, and 1 IB. the repeatability and consistency of the polished windows was significantly improved for the polished articles produced using the fixture, due at least in part to the more accurate pressure control provided by the fixture. Example 2

[0073] To determine the ability of the fixtures described herein to produce repeatable polishing pressures, the force detected by a load cell mounted in the fixture as described herein was recorded while polishing a workpiece to produce two separate polished regions. The measured f orce as a function of time is shown in FIG. 12. The two plateaus in FIG. 12 correlate to the two separate polished regions.

Example 3

[0074] 50 sample workpieces were polished using a fixture mounted on a CNC machine of the type described herein. The polished region profiles were measured in the x- and y-directions on a Zygo optical surface profiler, with an exemplary y-axis profile of a polished region shown in (a) in FIG. 13. DL and DR are the left and right endpoints of the diameter of the polished region, FL and FR are the left and right endpoints of the flat region of the polished region, C is the center point of the window, and F-peak is the highest point in the flat region of the polished region. Plot (b) in FIG. 13 shows a zoomed-in view of the flat region of the polished region (the dotted box in plot (a)) and shows an 8-order polynomial curve fit to the flat region profile. Plot (c) in FIG. 13 shows the difference in height (pm) after subtracting the polynomial curve fit from the measured profile. The dotted box in plot (c) outlines a sliding 0.525-mm section of the flat region. The maximum peak-to-valley (PV) deviation within this 0.525-mm section was measured as the section was moved across the flat region. For the polished region in plot (a), this maximum PV deviation was 87.3 nm.

[0075] Plot (d) in FIG. 13 is a graph of the maximum PV deviation within a 0.525-mm sliding section of the polished regions of the 50 polished workpieces, measured in both the x- and y-directions. The dotted box outlines the maximum PV deviation measured for the window shown in plots (a)-(c). The black line in plot (d) shows the average of the maximum PV deviation values (44 nm) and the shaded band shows the standard deviation (±14 nm).

[0076] The 0.525-mm region of each polished region was selected for the measurements because the field of view, at the user-facing surface of the polished region, for a typical laptop camera with a typical setback placed behind the glass is 0.525 mm.

[0077] It will be apparent to those skilled in the art that various modifications and variations can be made to the embodiments described herein without departing from the spirit and scope of the claimed subj ect matter. Thus, it is intended that the specification cover the modifications and variations of the various embodiments described herein provided such modification and variations come within the scope of the appended claims and their equivalents.