PATENT DOCUMENT

Publication Number: US-11680010-B2
Application Number: US-202016903896-A
Country: US
Kind Code: B2

Title: Evaluation of transparent components for electronic devices

Abstract:
Methods for evaluating a chemically strengthened housing component for an electronic device are disclosed. These methods may allow non-destructive determination of whether the chemical strengthening of the component meets specifications. Systems suitable for use with the methods are also disclosed.

Claims:
What is claimed is: 
     
       1. A method comprising:
 directing polarized light through a glass cover member, through a polarization analyzer, and onto a sensor, the polarized light directed through a first portion of the glass cover member and through a second portion of the glass cover member, the first portion of the glass cover member at least partially defining a curved boundary of an opening in the glass cover member and the second portion of the glass cover member located away from the opening; 
 obtaining, using the sensor, a first optical measurement of polarized light from the first portion of the glass cover member that is directed through the polarization analyzer and a second optical measurement of polarized light from the second portion of the glass cover member that is directed through the polarization analyzer; 
 determining a differential intensity value based on the first and the second optical measurements; 
 determining an estimated stress level of the first portion of the glass cover member, the estimated stress level based on the differential intensity value; 
 determining an estimated level of chemical strengthening of the second portion of the glass cover member based on the estimated stress level and a stress multiplier value that is determined based on an estimate of a curvature of a region of the curved boundary defined by the first portion of the glass cover member; 
 comparing the estimated level of chemical strengthening to a reference chemical strengthening range; and 
 determining whether the estimated level of chemical strengthening falls within the reference chemical strengthening range. 
 
     
     
       2. The method of  claim 1 , wherein:
 the glass cover member is part of an enclosure for a mobile phone; 
 the opening is elongated and provides a speaker port for an earpiece of the mobile phone; and 
 the curved boundary is located along an end of the opening. 
 
     
     
       3. The method of  claim 1 , further comprising:
 comparing the estimated stress level of the first portion of the glass cover member to a reference stress range; and 
 rejecting the glass cover member when the estimated stress level of the first portion of the glass cover member is outside the reference stress range. 
 
     
     
       4. The method of  claim 1 , further comprising:
 determining an estimated level of chemical strengthening of the first portion of the glass cover member; and 
 rejecting the glass cover member when the estimated level of chemical strengthening of the first portion of the glass cover member is outside the reference chemical strengthening range. 
 
     
     
       5. The method of  claim 1 , further comprising estimating a stress level of the second portion of the glass cover member based on the estimated stress level of the first portion of the glass cover member and the stress multiplier value. 
     
     
       6. The method of  claim 1 , wherein a radius of the curvature of the curved boundary is less than or equal to 1 mm. 
     
     
       7. The method of  claim 1 , wherein the sensor produces an image of at least the first portion and the second portion of the glass cover member. 
     
     
       8. The method of  claim 7 , wherein:
 the sensor is a first sensor and the image is a first image; and 
 the estimate of the curvature of the curved boundary is determined from a second image produced by a second sensor. 
 
     
     
       9. The method of  claim 7 , wherein the sensor is included in an image acquisition device of an optical inspection unit. 
     
     
       10. The method of  claim 9 , wherein: the first optical measurement of polarized light from the first portion of the glass cover member that is directed through the polarization analyzer provides a first intensity value; the second optical measurement of polarized light from the second portion of the glass cover member that is directed through the polarization analyzer; provides a second intensity value; and the differential intensity value is determined from the first and second intensity values. 
     
     
       11. The method of  claim 9 , wherein a computing device in communication with the optical inspection unit computes the estimated stress level and the estimated chemical strengthening level. 
     
     
       12. The method of  claim 9 , wherein:
 the optical inspection unit is a second optical inspection unit; and 
 a first optical inspection unit is used to obtain the estimate of the curvature of the region of the curved boundary. 
 
     
     
       13. The method of  claim 12 , wherein the first optical inspection unit is used to acquire an image of the curved boundary of the opening. 
     
     
       14. A method comprising:
 forming an interference pattern by passing polarized light through a chemically strengthened glass cover member and through a polarization analyzer, the polarized light directed through at least a first portion of the chemically strengthened glass cover member and through a second portion of the chemically strengthened glass cover member; 
 receiving the interference pattern at a light sensor; 
 analyzing the interference pattern, the analyzing comprising:
 determining a first intensity value corresponding to polarized light from the first portion of the chemically strengthened glass cover member that is directed through the polarization analyzer, the first portion of the chemically strengthened glass cover member at least partially defining a curved boundary of an opening in the chemically strengthened glass cover member; and 
 determining a second intensity value corresponding to polarized light from the second portion of the chemically strengthened glass cover member that is directed through the polarization analyzer, the second portion of the chemically strengthened glass cover member located away from the opening; 
 
 determining an estimated first stress level of the first portion of the chemically strengthened glass cover member based on a difference between the first intensity value and the second intensity value; 
 determining an estimated second stress level of the second portion of the chemically strengthened glass cover member based on the estimated first stress level and a stress multiplier value estimated based on a curvature of a region of the curved boundary defined by the first portion of the chemically strengthened glass cover member; 
 comparing the estimated second stress level to a reference stress range; and 
 determining whether the estimated second stress level is within the reference stress range. 
 
     
     
       15. The method of  claim 14 , wherein:
 the opening is elongated and comprises two curved end portions and a straight portion extending between the two curved end portions; and 
 the curved boundary is positioned within one of the two curved end portions of the opening. 
 
     
     
       16. The method of  claim 14 , wherein a distance between the second portion of the chemically strengthened glass cover member and the opening is greater than or equal to a thickness of the chemically strengthened glass cover member. 
     
     
       17. The method of  claim 14 , further comprising computing, from the first intensity value, an estimated phase difference of the polarized light from the first portion of the chemically strengthened glass cover member. 
     
     
       18. The method of  claim 14 , wherein:
 the light sensor produces an image; and 
 the difference between the first intensity value and the second intensity value produces a contrast difference in the image. 
 
     
     
       19. The method of  claim 18 , wherein the reference stress range is a second reference stress range and the method further comprises:
 comparing the estimated first stress level to a first reference stress range; and 
 determining whether the first estimated first stress level is within the first reference stress range.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application is a non-provisional patent application and claims the benefit of U.S. Provisional Patent Application No. 62/872,131, filed Jul. 9, 2019 and titled “Evaluation of Transparent Components for Electronic Devices,” the disclosure of which is hereby incorporated by reference in its entirety. 
    
    
     FIELD 
     The described embodiments relate generally to evaluation of transparent components for electronic devices. More particularly, the present embodiments relate to evaluation of chemically strengthened transparent components which include a geometric feature such as an opening. 
     BACKGROUND 
     Electronic device enclosures may include metal, plastic or glass parts. Enclosure parts with resistance to scratching and/or impact can provide durability to the enclosure. In some cases, glass enclosure parts, such as a cover glass, may be chemically strengthened in order to improve their durability. The techniques, systems, and devices described herein are directed to evaluating chemically strengthened transparent components for electronic device enclosures. 
     SUMMARY 
     Methods for evaluating a chemically strengthened transparent component for an electronic device are disclosed herein. The transparent component may be a glass cover member or another glass component of the enclosure. The methods disclosed herein may allow non-destructive estimation of one or more stress levels in the transparent component produced by chemical strengthening. The methods may also be used to evaluate an overall level of chemical strengthening of the transparent component. Systems suitable for use with the methods are also disclosed. 
     The methods disclosed herein are particularly suited for evaluating a transparent component including an opening or other geometric feature which modifies the chemical strengthening of the transparent component. The opening or other geometric feature can lead to non-uniformity of the residual stresses resulting from chemical strengthening. The non-uniformity of the residual stresses in the transparent component can produce one or more optical effects under certain lighting and/or viewing conditions (e.g., when viewed with polarized light). 
     The methods described herein may allow estimation of a localized stress level in the vicinity of the opening or other geometric feature and/or a localized stress level away from the opening or other geometric feature. In some cases, the localized stress level in the vicinity of an opening may be greater than a localized stress level away from the opening. As an example, the localized stress level in the vicinity of the opening may be equal to the product of the localized stress level away from opening and a stress multiplier value. The stress multiplier value may depend on a shape of the geometric feature. In some cases, the stress multiplier value may depend on a curvature value of the geometric feature. 
     The methods disclosed herein use non-destructive optical techniques to assess one or more localized stress levels in the chemically strengthened transparent component. In some cases, the optical technique forms an image of the chemically strengthened transparent component and an intensity or other optical property of a given region of the image relates to the localized stress level in a corresponding portion of the transparent component. In some examples, one or more color values of a given region of the image can relate to the localized stress level in the corresponding portion of the transparent component. 
     In some cases, determining the localized stress level in one portion of the transparent component can allow estimation of the localized stress level in another portion of the transparent component. For example, determining the localized stress level of a portion of the transparent component near a geometric feature (e.g., an opening) can allow estimation of another portion of the transparent component (e.g., away from the geometric feature) by dividing the determined localized stress level by a stress multiplier value determined for the geometric feature. As another example, determining the localized stress level of a portion of the transparent component away from the geometric feature can allow estimation of a portion of the transparent component near the geometric feature by multiplying the determined localized stress level by a stress multiplier value for the geometric feature. 
     In some embodiments, the disclosure provides a method of estimating a chemical strengthening level of a glass cover member of an electronic device. The method comprises directing polarized light through the glass cover member, through a polarization analyzer, and onto a sensor to produce at least one optical measurement of the glass cover member. The method further comprises determining a differential intensity value from at least one optical measurement of a first portion and a second portion of the glass cover member, the first portion at least partially defining a curved boundary of an opening in the glass cover member and the second portion located away from the opening. The method further comprises estimating a localized stress level of the first portion based on the differential intensity value, obtaining an estimate of a curvature of the curved boundary, determining a stress multiplier value based on the estimate of the curvature, and estimating a chemical strengthening level of the glass cover member based on the localized stress level and the stress multiplier value. 
     The disclosure also provides a method of estimating a stress level in a chemically strengthened glass cover member. The method comprises forming an interference pattern by passing polarized light through the chemically strengthened glass cover member and through a polarization analyzer. The method further comprises receiving the interference pattern at a light sensor and analyzing the interference pattern. The analyzing comprises determining an intensity value corresponding to a first portion of the chemically strengthened glass cover member, the first portion at least partially defining a curved boundary of an opening in the chemically strengthened glass cover member and estimating a first localized stress level of the first portion based on the intensity value. The method further comprises estimating a stress multiplier value based on a curvature of the curved boundary and estimating a second localized stress level of a second portion of the chemically strengthened glass cover member, the second portion located away from the opening and the operation of estimating the second localized stress level being based on the first localized stress level and the stress multiplier value. 
     The disclosure also provides a system for estimating a stress level in a glass cover member. The system comprises a first optical inspection unit comprising a first light source, a first image sensor, and a first processor. The first optical inspection unit is configured to produce a first image of at least a first region of a glass cover member using the first light source and the first image sensor, the first region including an opening defined by the glass cover member. The first optical inspection unit is further configured to determine a curvature value of the opening from the first image using the first processor. The system further comprises a second optical inspection unit comprising a second light source, a polarizer, a polarization analyzer, a second image sensor, and a second processor. The second optical inspection unit is configured to produce polarized light using the second light source and the polarizer and direct the polarized light through at least a second region of the glass cover member, through the polarization analyzer, and onto the second image sensor, thereby forming a second image of at least the second region of the glass cover member. In addition, the second optical inspection unit is configured to determine a first intensity value of the second image using the second processor, the first intensity value corresponding to a first portion of the glass cover member, the first portion at least partially defining a curved boundary of the opening in the glass cover member, and determine a second intensity value of the second image using the second processor, the second intensity value corresponding to a second portion of the glass cover member and the second portion located away from the opening. The system further comprises a computing system comprising a memory containing instructions; and a third processor. The third processor is configured to execute the instructions and thereby cause the computing system to perform operations including receiving the curvature value from the first optical inspection unit, estimating a stress multiplier value based on the curvature value, estimating a localized stress level in the first portion of the glass cover member based on a difference between the first intensity value and the second intensity value, and estimating a chemical strengthening level of the glass cover member based on the localized stress level and the stress multiplier value. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure will be readily understood by the following detailed description in conjunction with the accompanying drawings, wherein like reference numerals designate like elements. 
         FIG.  1 A  shows a front view of an example electronic device. 
         FIG.  1 B  shows an example of a rear view of the electronic device of  FIG.  1 A . 
         FIG.  1 C  shows an example of a cross-section view of the electronic device of  FIGS.  1 A and  1 B . 
         FIG.  2    shows an example of a glass cover member having an opening. 
         FIG.  3    shows a detail view of a glass cover member having an opening. 
         FIG.  4    shows another example of a glass cover member having an opening. 
         FIG.  5    shows an example cross-section view of a glass cover member. 
         FIG.  6    shows another example cross-section view of a glass cover member. 
         FIG.  7    schematically shows transmission of light through a chemically strengthened glass cover member. 
         FIG.  8    schematically shows elements of an optical system for evaluating a chemically strengthened glass cover member. 
         FIG.  9    shows an example of an image of a chemically strengthened glass cover member. 
         FIG.  10    shows a flow chart of a process for evaluating a glass component. 
         FIG.  11    shows a flow chart of another process for evaluating a glass component. 
         FIG.  12    shows a system for evaluating a chemically strengthened glass cover member. 
         FIG.  13    shows a block diagram of components of an electronic device. 
     
    
    
     The use of cross-hatching or shading in the accompanying figures is generally provided to clarify the boundaries between adjacent elements and also to facilitate legibility of the figures. Accordingly, neither the presence nor the absence of cross-hatching or shading conveys or indicates any preference or requirement for particular materials, material properties, element proportions, element dimensions, commonalities of similarly illustrated elements, or any other characteristic, attribute, or property for any element illustrated in the accompanying figures. 
     Additionally, it should be understood that the proportions and dimensions (either relative or absolute) of the various features and elements (and collections and groupings thereof) and the boundaries, separations, and positional relationships presented therebetween, are provided in the accompanying figures merely to facilitate an understanding of the various embodiments described herein and, accordingly, may not necessarily be presented or illustrated to scale, and are not intended to indicate any preference or requirement for an illustrated embodiment to the exclusion of embodiments described with reference thereto. 
     DETAILED DESCRIPTION 
     Reference will now be made in detail to representative embodiments illustrated in the accompanying drawings. It should be understood that the following descriptions are not intended to limit the embodiments to one preferred implementation. To the contrary, the described embodiments are intended to cover alternatives, modifications, and equivalents as can be included within the spirit and scope of the disclosure and as defined by the appended claims. 
     The following disclosure relates to methods for evaluating a chemically strengthened transparent component for an electronic device. The transparent component may be a glass cover member, another glass component, or a glass ceramic component of the enclosure. The non-destructive optical methods disclosed herein can be used to assess whether a chemical strengthening level of the transparent component falls within an acceptable range. The ability to identify and reject unacceptably chemically strengthened components can help control the quality of the assembled electronic devices. In addition, the ability to identify a transparent component having a chemical strengthening level outside the acceptable range can improve control of the chemical strengthening process. 
     In embodiments described herein the chemically strengthened transparent component includes non-uniform residual stresses due at least in part to an opening or other geometric feature in the transparent component. The non-uniformity of the residual stresses in the transparent component can produce one or more optical effects under certain lighting and/or viewing conditions. For example, the transparent component may reflect polarized light non-uniformly and produce an optical effect conventionally referred to as (optical) anisotropy or iridescence. In some cases, the methods disclosed herein can be used to predict the amount of optical anisotropy or iridescence produced under particular viewing conditions. 
     In addition, the methods disclosed herein can be used to determine residual stress levels in the transparent component. In some cases, the methods disclosed herein can determine whether a localized stress level near an opening or other geometric feature of the transparent component is unacceptably high. If the localized stress level in the transparent component is unacceptably high near the geometric feature, a level of chemical strengthening near the geometric feature may be unacceptably high and this portion of the transparent component may be more susceptible to some forms of damage. In addition, the methods disclosed herein may be used to determine whether a localized stress level away from the opening or other geometric feature is unacceptably low. If the localized stress level in the transparent component is unacceptably low, the transparent component may be susceptible to cracking. 
     Estimates of a localized stress level at one or more locations of the transparent component may be determined at least in part using a photoelastic technique. The residual stresses within the transparent component due to the chemical strengthening process typically cause stress birefringence. As a result, polarized light transmitted through or reflected from the transparent component may be used to form a photoelastic pattern, which may be an interference pattern. In some cases, the methods disclosed herein form an image of the transparent component. One or more intensity values of the image may be measured in order to determine one or more localized stress levels in the transparent component. The estimates of the one or more localized stress levels may in turn be used to estimate a level of chemical strengthening of the transparent component. 
     In some cases, the disclosure describes methods and systems used to evaluate glass components. The disclosure provided herein with respect to methods and systems used to evaluate glass components may also be applicable to other types of ion-exchangeable transparent components. For example, the disclosure provided herein may also be applicable to ion-exchangeable glass ceramic components or components including an ion-exchangeable glass and an ion-exchangeable glass ceramic. 
     These and other embodiments are discussed below with reference to  FIGS.  1 A- 13   . However, those skilled in the art will readily appreciate that the detailed description given herein with respect to these figures is for explanatory purposes only and should not be construed as limiting. 
       FIG.  1 A  shows a front view of an example electronic device  100  including a glass component. The electronic device  100  may be a mobile telephone (also referred to as a mobile phone). In additional embodiments, the electronic device  100  may be a notebook computing device (e.g., a notebook), a tablet computing device (e.g., a tablet), a portable media player, a wearable device, or another type of portable electronic device. The electronic device  100  may also be a desktop computer system, computer component, input device, appliance, or virtually any other type of electronic product or device component. 
     As shown in  FIG.  1 A , the electronic device  100  has an enclosure  110  including a cover assembly  122 . The cover assembly  122  may include a glass component in the form of a glass cover member  152  (also shown in  FIG.  1 C ). The cover assembly  122  may also include one or more coatings on the glass cover member  152 , such as a smudge-resistant coating on an exterior surface of the glass cover member  152 . The description provided herein with respect to examples of glass cover members (e.g., glass cover member  152 ) applies more generally to other types of glass enclosure components and other types of ion-exchangeable transparent enclosure components. 
     As shown in  FIG.  1 A , the glass cover member  152  defines an opening  172  (which may also be referred to as a hole). In general, an opening may be provided in the glass cover member  152  or other transparent component to facilitate input to or output from a device component such as a microphone, a camera component, and the like. In the example of  FIG.  1 A , the opening  172  may provide a speaker port for an earpiece of the electronic device  100 . Examples of openings are discussed in further detail with respect to  FIGS.  2 - 4   . The description provided with respect to  FIGS.  2 - 4    is generally applicable herein and, for brevity, is not repeated here. 
     The glass cover member  152  is typically chemically strengthened through ion exchange. Chemical strengthening of glass cover members is described in further detail with respect to  FIGS.  3 ,  5 , and  6   . The description provided with respect to  FIGS.  3 ,  5 , and  6    is generally applicable herein and, for brevity, is not repeated here. For brevity, a chemically strengthened glass component such as a chemically strengthened glass cover member may simply be referred to herein as a glass component or glass cover member. 
     In some embodiments the cover assembly  122  may be described as a glass cover. More generally, the cover assembly  122  may be formed from multiple layers. For example, a multilayer cover assembly may include one or more glass cover members, glass ceramic cover members, composite cover members including a glass and a glass ceramic, polymer cover members, and/or various coatings and layers. In some cases, a cover member may take the form of a sheet. As examples, a coating or layer of a cover assembly may include a smudge-resistant layer, an anti-reflective layer, a decorative layer on an interior surface of a cover member, an adhesive layer, or a combination thereof. 
     Typical cover assemblies herein are thin, typically less than 5 mm in thickness, and more typically less than 3 mm in thickness. In some aspects, a glass cover member (or other cover member) included in a cover assembly can have a thickness from about 0.1 mm to 2 mm, from 0.5 mm to 2 mm, or from 0.2 mm to 1 mm. 
     The cover assembly  122  may at least partially define a front surface  102  of the electronic device  100  (see  FIG.  1 C ). The cover assembly  122  is positioned over the display  144  and may define a transparent portion positioned over the display  144  (indicated by the dashed line in  FIG.  1 A ). The enclosure  110  may at least partially surround the display  144 . 
     As shown in  FIG.  1 A , the enclosure  110  further includes a housing  112  (which may also be referred to as a housing member). The cover assembly  122  may be coupled to the housing  112 . For example, the cover assembly  122  may be coupled to the housing  112  with an adhesive, a fastener, an engagement feature, or a combination thereof. The housing  112  may be formed from a metal, a glass, a ceramic, a plastic, or a combination thereof. 
     The housing  112  may at least partially define a side surface  106  of the electronic device  100  (see  FIG.  1 C ). Generally, a housing  112  may include one or more metal members or one or more glass members. As shown in  FIG.  1 A , the housing  112  is formed from a series of metal segments ( 114 ,  116 ) that are separated by polymer or dielectric segments  115  that provide electrical isolation between adjacent metal segments. One or more of the metal segments ( 114 ,  116 ) may be coupled to internal circuitry of the electronic device  100  and may function as an antenna for sending and receiving wireless communication. 
       FIG.  1 B  shows an example of a rear view of the electronic device  100  of  FIG.  1 A . The enclosure  110  further includes a cover assembly  124 . The cover assembly  124  defines a rear surface  104  of the electronic device  100  (see  FIG.  1 C ). The enclosure  110 , the housing  112 , the metal segments  114  and  116 , and the polymer or dielectric segments  115  are as previously described for  FIG.  1 A . 
     The cover assembly  124  may include a glass cover member  154 . As shown in  FIG.  1 B , glass cover member  154  includes an opening  174  configured to surround a window  117  and one or more camera assemblies may be placed below the window  117 . In other embodiments, the glass cover member  154  may not include an opening or may include multiple openings. 
       FIG.  1 C  shows an example of a cross-section view of the electronic device  100  of  FIGS.  1 A and  1 B . The cross-section may be taken along A-A of  FIG.  1 A . As previously described, the enclosure  110  of the electronic device  100  includes the cover assembly  122  at the front and the cover assembly  124  at the rear of the electronic device  100 . 
     The electronic device  100  further includes a display  144  and a touch sensor  142  provided below the front cover assembly  122 . The display  144  may be a liquid-crystal display (LCD), a light-emitting diode (LED) display, an LED-backlit LCD display, an organic light-emitting diode (OLED) display, an active layer organic light-emitting diode (AMOLED) display, and the like. The touch sensor  142  may be configured to detect or measure a location of a touch along the exterior surface of the front cover assembly  122 . Touch sensors and displays are described in more detail below with respect to  FIG.  13    and that description is generally applicable herein. 
     As shown in  FIG.  1 C , the cover assembly  122  defines a front surface  102  and the cover assembly  124  defines a rear surface  104  of the electronic device  100 . The housing  112  may at least partially define a side surface  106  of the electronic device  100 . The housing  112  may also at least partially define a side wall of the electronic device, the side wall at least partially enclosing the internal cavity  105 . 
     As previously described with respect to  FIG.  1 B , a window  117  may be positioned within an opening  174  formed in a glass cover member and a camera assembly positioned below the window  117 . As schematically shown in  FIG.  1 C , additional components  146  may also be included within the interior volume  105  of the electronic device  100 . These additional components may comprise one or more of a processing unit, control circuitry, memory, an input/output device, a power source, a network communication interface, an accessory, and a sensor. Components of a sample electronic device are described in more detail below with respect to  FIG.  13    and that description is generally applicable herein. 
       FIG.  2    shows an example of a glass cover member  252  defining an opening  272 . Typically the opening  272  extends through a thickness of the glass cover member  252 . As shown in  FIG.  2   , an exterior surface  255  of the glass cover member  252  defines a rectangular shape with rounded corners. The rectangular shape has a length L 1  and width W 1 , with the length L 1  being longer than the width W 1 . The opening  272  is positioned so a longitudinal axis of the opening is aligned with the width W 1  of the rectangular shape. 
     As shown in  FIG.  2   , the glass cover member  252  defines a boundary  262  of the opening  272 . The shape of the boundary  262  defines a shape of the opening  272 . As shown in  FIG.  2   , at least a portion of the boundary  262  is curved and the curved portion is located along an end of the opening (also referred to herein as an end portion). For example, the boundary  262  may define a stadium shape at the external surface  255  of the glass cover member  252 . The opening  272  has a length X 1  and a height Y 1 , and is elongated, with the length X 1  being greater than the height Y 1 . As shown in  FIG.  2   , the length X 1  is aligned with the width W 1  of the glass cover member  252 . In additional examples, a length or diameter of an opening may be aligned with or angled with respect to a length or width of the glass cover member  252 . Additional description of features of the opening  272  is provided with respect to the detail view of  FIG.  3    and, for brevity, is not repeated here. 
     It should be understood that the shape of the opening  272  is not limited to the example of  FIG.  2   , but may be any shape suitable for its intended purpose. For example, an opening  272  may have a shape at the exterior surface  255  of the glass cover member  252  which is circular, oval, a rounded square (a square with rounded corners), a rounded rectangle, and the like. 
     In addition, the shape of the glass cover member  252  is not limited to the example of  FIG.  2   , but may be any shape suitable for its intended purpose. Although the glass cover member  252  is shown in  FIG.  2    as being substantially planar, the principles described herein also relate to glass components and glass cover members including one or more curved surfaces. In embodiments, a glass component such as a glass cover member may be three-dimensional. For example, the glass component may define a peripheral portion that is not coplanar with respect to a central portion. The peripheral portion may, for example, define a side wall of a device housing or enclosure, while the central portion defines a front surface (which may define a transparent window that overlies a display). 
     The glass components described herein, such as glass cover member  252 , may comprise a glass material. The glass material may be a metal oxide-based material such as a silica-based material. The glass material of the glass cover member may have a network structure, such as a silicate-based network structure. For example, the glass material may comprise an aluminosilicate glass or a boroaluminosilicate glass. As used herein, an aluminosilicate glass includes the elements aluminum, silicon, and oxygen, but may further include other elements. Similarly, a boroaluminosilicate glass includes the elements boron, aluminum, silicon, and oxygen, but may further include other elements. 
     The glass material may be ion-exchangeable. For example, an aluminosilicate glass or a boroaluminosilicate glass may further include monovalent or divalent ions which compensate charges due to replacement of silicon ions by aluminum ions. Suitable monovalent ions include, but are not limited to, alkali metal ions such as Li + , Na + , or K + . Suitable divalent ions include alkaline earth ions such as Ca 2+  or Mg 2+ . The glass material of the glass cover member may be ion exchangeable. 
       FIG.  3    shows a detail view of a glass cover member  352  having a boundary  362  which defines an opening  372 . The opening  372  may be an example of the opening  272  of  FIG.  2    and for brevity those details are not repeated here. 
     The boundary  362  may include boundary portions  364  set apart from each other and defining a central portion  374  of the opening. The boundary may also include boundary portions  366  defining end portions  376  of the opening  372 . The end portions  376  of the opening  372  are curved and may also be referred to herein as curved end portions  376 . The central portion  374  of the opening extends between the two curved end portions  376 . As shown in  FIG.  3   , the central portion  374  may define a “straight” portion (e.g., a rectilinear portion) of the opening  372 . 
     As shown in  FIG.  3   , the portions  366  are curved portions of the boundary  362 . Each of the curved portions  366  is located along an end portion  376  of the opening  372 . The curved portions  366  may be described by a radius of curvature R (shown in the plane defined by the surface  355  of the glass cover member  352 ). In some cases, the curved portions  366  may have a substantially constant radius of curvature, so that the curved portions are semi-circular. In other cases, the curved portions  366  may be characterized by a minimum radius of curvature. The radius of curvature R may be less than or equal to 2 mm, less than or equal to 1.5 mm, less than or equal to 1 mm, less than or equal to 500 microns, from 100 microns to 1 mm, or from 50 microns to 500 microns. For simplicity, a curved portion  366  of the boundary  362  may also be referred to herein as a curved boundary. 
     As shown in  FIG.  3   , the boundary portions  364  have a curvature less than that of the curved boundary portions  366 . In some embodiments, the boundary portions  364  may be substantially “straight” or rectilinear at the surface  355  of the glass cover member  352  (and planar in three dimensions). 
     Typically the glass cover member  352  is chemically strengthened as the result of one or more ion-exchange operations. Therefore, a chemically strengthened glass cover member may also be referred to herein as an ion-exchanged glass cover member. During the ion exchange operation, ions present in the glass material may be exchanged for larger ions in a region extending from a surface of the glass cover member. For example, an ion-exchangeable glass material may include monovalent or divalent ions such as alkali metal ions (e.g., Li + , Na + , or K + ) or alkaline earth ions (e.g., Ca 2+  or Mg 2+ ) which may be exchanged for other alkali metal or alkaline earth ions. If the glass member comprises sodium ions, the sodium ions may be exchanged for potassium ions. Similarly, if the glass member comprises lithium ions, the lithium ions may be exchanged for sodium ions and/or potassium ions. Similar ion-exchange processes may be used to chemically strengthen other types of ion-exchangeable transparent components, such as glass ceramic components. 
     The ion exchange operation typically creates residual stress in the glass cover member. For example, exchange of ions present in the glass material for larger ions may produce residual compressive stress within the ion-exchanged region extending from the surface of the glass cover member  352 . A tensile stress region may also be formed within the glass cover member  352 . Additional description of compressive stress and tensile stress regions formed within the glass cover member is provided with respect to  FIGS.  5  and  6    and, for brevity, is not repeated here. In some cases, the residual stresses in the glass cover member  352  due to chemical strengthening can produce a double refraction effect which can be measured with an optical photoelastic technique. 
     The residual stresses due to ion exchange may be different in a portion  357  of the glass cover member  352  near the opening  372  than in a portion  358  of the glass cover member  352  away from the opening  372  (and the sides  354  of the glass cover member  352 ). In some cases, at least some of the residual stresses due to ion exchange may be greater at or near the curved end portions  376  of the opening than away from the opening  372 . In such cases, the residual stresses may be viewed as being concentrated at or near the curved end portions  376 . 
     The directions of the principal in-plane stresses may also be different in different portions of the glass cover member  352  as shown schematically in  FIG.  3   . At the portion  357  of the glass cover member  352  (near a curved portion  366  of the boundary  362 ), a principal stress σ R  is in a radial direction and a principal stress σ T  is in a tangential direction. The principal stress σ R  may be zero at the boundary portion  366 . At the portion  358  of the glass cover member  352 , a principal stress σ X  may be aligned with the x axis (e.g., aligned with the width W 1  of the glass cover member  252  as shown in  FIG.  2   ) and a principal stress σ Y  may be aligned with the y axis (e.g., aligned with the length L 1  of the glass cover member  252  as shown in  FIG.  2   ). 
     Information about differences in stress states between different portions of the glass cover member  352  can be obtained using a photoelastic technique. In particular, the refractive index of a given portion of the glass cover member  352  (e.g., the portion  357  or the portion  358 ) may depend upon the stress state and the principal stress directions of that portion. Use of optical photoelastic techniques to obtain information about stress states of a glass cover member is described in more detail with respect to  FIGS.  7 - 9    and, for brevity, that description is not repeated here. 
       FIG.  4    shows another example of a glass cover member  452  defining an opening  472 . As shown in  FIG.  4   , an exterior surface  455  of the glass cover member  452  defines a rectangular shape with rounded corners. The rectangular shape has a length L 2  and width W 2 . 
     The glass cover member  452  defines a boundary  462  around the opening  472 . The opening  472  may have a shape at least partially defined by the shape of the boundary  462 . As shown in  FIG.  4   , the boundary  462  and the opening  472  define a rounded rectangular shape (at the exterior surface  455 ). The opening  472  may have a width X 2  and a height Y 2 . As shown in  FIG.  4   , the height Y 2  is greater than the width X 2  of the opening  472 . 
     The boundary  462  may include portions  464  which largely define the sides of the rounded rectangular shape. The boundary  462  also includes rounded corner portions  466 . The rounded corner portions may be described by a curvature (and a radius of curvature). As shown in  FIG.  4   , the boundary portions  464  have a curvature less than that of the rounded corner portions  466 . In some embodiments, the boundary portions  464  may be substantially “straight” or rectilinear at the exterior surface  455  (and planar in three dimensions). 
     In some cases, the residual stresses due to ion exchange are different in a portion of the glass cover member  452  near the opening  472  than in a portion of the glass cover member  452  away from the opening  472 . For example, at least some of the residual stresses due to ion exchange may be greater at or near the rounded corners  466  of the boundary  462  than away from the opening  472 . In such cases, the residual stresses may be viewed as being concentrated at or near the rounded corners  466  of the boundary  462 . 
     As previously described with respect to  FIG.  2   , the shape of the opening  472  and the shape of the glass cover member  452  are not limited to those shown in  FIG.  4    and may be any of the shapes previously described with respect to  FIG.  2   . For brevity, that description is not repeated here. 
       FIG.  5    shows an example of a partial cross-section view of a glass cover member  552  and schematically illustrates residual stress regions formed in the glass cover member as a result of chemical strengthening. The cross-section of  FIG.  5    may be located away from any openings in the glass cover member  552  and may be an example of a partial cross-section of glass cover member  252  of  FIG.  2    (along line B-B and in detail area  1 - 1 ). 
     As shown in  FIG.  5   , a compressive stress region  594  extends from the exterior surface  555  and a compressive stress region  596  extends from the interior surface  556  of the glass cover member  552  (not shown to scale). A tensile stress region  595  is positioned between the compressive stress regions  594  and  596 . The compressive stress regions  594  and  596  may have a biaxial compressive stress state. Compressive stress regions  594  and  596  may also be referred to herein as compressive stress layers and tensile stress region may also be referred to herein as a tensile stress layer. The compressive stress region  594  may have a depth D 1 , the compressive stress region may have a depth D 2 , and the glass cover member  552  may have a thickness D. In some cases, the depths D 1  and D 2  may be substantially equal. In other cases, the depths D 1  and D 2  may differ. For example, the depth D 1  may be greater than the depth D 2  to provide increased resistance to cracking at the exterior surface  555 . 
     As previously discussed with respect to  FIG.  3   , the compressive stress regions  594  and  596  may be formed as a result of an ion exchange operation. The ion exchange may occur within a first ion-exchanged region extending from the exterior surface  555  and a second ion-exchanged region extending from the interior surface  556  of the glass cover member  552 . The ion exchange leads to formation of compressive stress regions  594  and  596  within these ion-exchanged regions. The compressive stress regions  594  and  596  may be enriched in the larger ions as compared to the glass material in the tensile stress region  595 . The ion exchange operation may take place at a temperature above room temperature but at a temperature below the strain point of the glass. 
       FIG.  6    shows another example cross-section view of a glass cover member  652  which schematically illustrates residual stress regions formed in the glass cover member  652  as a result of chemical strengthening. The cross-section of  FIG.  6    may intersect an opening  672  in the glass cover member  652  and may be an example of a cross-section of glass cover member  352  along line C-C in  FIG.  3   . The boundary  662  defines the opening  672 . 
     As shown in  FIG.  6   , the stress state near the opening  672  is different than the stress state shown in  FIG.  5   . As schematically shown in  FIG.  6   , a compressive stress region  694  extends from the exterior surface  655 , a compressive stress region  696  extends from the interior surface  656 , and a compressive stress region  698  extends from a boundary  662  of the glass cover member  652  (not shown to scale). A tensile stress region  695  is bounded, at least in part, by the compressive stress regions  694 ,  696 , and  698 . As schematically illustrated in  FIG.  6   , a portion of the glass cover member  652  near the boundary  662  may have a triaxial stress state. The compressive stress regions  694 ,  696 , and  698  may be formed by an ion-exchange process as previously described for  FIG.  5    and, for brevity, that description is not repeated here. 
     As previously discussed with respect to  FIG.  3   , the presence of the opening  672  may concentrate residual stress in the vicinity of the opening  672 . The concentration of residual stress is schematically shown in  FIG.  6    by the different depths of the compressive stress regions  694 ,  696 , and  698 . In the example of  FIG.  6   , the depth of the compressive stress region is greater at the boundary  662  and at the transition between the boundary  662  and the surfaces  655  and  656  than farther away from the boundary  662 . A stress multiplier value may be used to characterize the stress concentration effect. A stress multiplier value may also be referred to herein as a stress concentration factor. The stress multiplier value may be estimated based on the geometry of the opening  672  (and the boundary  662 ). For example, a stress multiplier value at or near a curved end portion of the opening  672  may be estimated based on a curvature value (or a radius of curvature) of the corresponding curved portion of the boundary  662 . 
     Other geometric features may also lead to a concentration of residual stress and a stress multiplier value may be estimated for these geometric features based on the geometry of these geometric features. For example, a stress multiplier for the opening shape of  FIG.  4    may be based upon a curvature value (or a radius of curvature) at the rounded corners. Estimation of the stress multiplier value is discussed in further detail with respect to  FIG.  9   , and for brevity, that discussion is not repeated here. 
     As previously discussed, optical photoelastic techniques can be used to obtain information about stress states of a chemically strengthened glass cover member. In some cases, the optical photoelastic techniques include an operation of directing polarized light through the chemically strengthened glass cover member. Changes in the polarization of at least some of the light passing through the glass cover member can produce optical effects which can provide information about the stress states. The polarized light may directed through the chemically strengthened glass cover member in a direction aligned with the thickness of the chemically strengthened glass cover member. 
       FIG.  7    schematically illustrates a change in the polarization of light directed through a chemically strengthened glass cover member  752 . In some cases, the light emerging from the chemically strengthened glass cover member  752  includes polarization components which are out of phase with each other. The change in the polarization of the light emerging from the chemically strengthened glass cover member  752  may result from stress birefringence (as previously discussed with respect to  FIG.  3   ). For purposes of illustration,  FIG.  7    shows transmission of a single ray of light through portion  758  of the glass cover member  752 . The portion  758  is located away from the opening  772  in the glass cover member  752 . 
     In the example of  FIG.  7   , a ray  781  is directed onto the glass cover member  752 . The light from ray  781  is transmitted through a portion  758  of the glass cover member  752 . The polarization of the ray  781  is modified as it is transmitted through the portion  758  and emerges from the glass cover member as ray  782 . In the example of  FIG.  7   , the ray  781  is linearly polarized with polarization E 1  and the ray  782  is elliptically polarized with polarization E 2  due to the difference in phase. 
     The chemically strengthened glass cover member  752  may be an example of glass cover members  152 ,  252 ,  352 , or any other glass cover members described herein and, for brevity, the description of these glass cover members is not repeated here. 
     The optical photoelastic techniques used herein may include directing polarized light through a polarization analyzer after directing the polarized light through the chemically strengthened glass cover member. However, in some cases polarized light reflected from the chemically strengthened glass cover member may be directed through the polarization analyzer. In these cases, a reflective backing may optionally be provided behind the chemically strengthened glass cover member. The light emerging from the polarization analyzer may be used to obtain information about the stresses present in the chemically strengthened glass cover member. For example, the light emerging from the polarization analyzer may be directed onto a sensor, as schematically illustrated in  FIG.  8   . One or more optical measurements provided by the sensor may then be used to obtain information about one or more stress states in the chemically strengthened glass cover member. When the light is reflected from the chemically strengthened glass cover, the optical measurement may effectively be an optical anisotropy measurement. 
       FIG.  8    schematically shows elements of an optical system  800  for evaluating a chemically strengthened glass cover member  852 . Some or all of the elements of optical system  800  may be included in the system  1200  of  FIG.  12   . In the optical system of  FIG.  8   , polarized light is directed onto and through the chemically strengthened glass cover member  852 , through a polarization analyzer  885 , and onto a sensor  887 . The optical system  800  further includes a light source  881  and a polarizer  883  for generating the polarized light. The polarized light may be directed onto and through a region of the chemically strengthened glass cover member  852 . The region may be less than an entirety of the chemically strengthened glass cover member  852 . The region may include a first portion and a second portion of the chemically strengthened glass cover member  852 , with the first portion at least partially defining a geometric feature, such as an opening, of the chemically strengthened glass cover member  852   
     The optical system  800  includes a light source  881 . The light source may predominantly produce light in a narrow band of wavelengths (e.g., a green fluorescent lamp) or may produce light essentially comprising a single wavelength (e.g., a laser). In addition, the light source may produce light covering a wider spectrum, such as the visible spectrum of light (e.g., a “white” fluorescent lamp). In some cases the light source may produce light in the form of a beam or one more lenses may be used to form a beam from the light before it enters the chemically strengthened glass cover member. The beam may have a diameter or width greater than or equal to that of the glass cover member or of the regions(s) of the glass cover member to be analyzed. In other cases, the light entering the chemically strengthened glass cover member need not form a beam. For example, diffuse light may be directed onto the chemically strengthened glass cover member. The description provided herein with respect to light source  881  is generally applicable to light sources as described herein, including the light sources of system  1200  of  FIG.  12   . 
     As shown in  FIG.  8   , the optical system  800  further includes a polarizer  883 . The light source  881  in combination with the polarizer  883  produces polarized light. As shown in  FIG.  8   , the polarizer  883  is a linear polarizer having a polarization orientation  884  at an angle θ with respect to the y axis. Alternately, the polarizer  883  may be a circular polarizer. 
     The optical system  800  also includes a polarization analyzer  885 . The polarization analyzer  885  may include an additional polarizer. As previously discussed with respect to  FIG.  7   , the polarization of the light emerging from the chemically strengthened glass cover member  852  may be different than the polarization of the light entering the chemically strengthened glass cover member  852 . The polarization analyzer  885  may be used to “combine” polarization components of the light. For example, the polarization components of the light may be combined into a single plane. Therefore, the polarization of the light emerging from the polarization analyzer may be different than the polarization of the light entering the polarization analyzer. 
     The light emerging from the polarization analyzer  885  may be used to obtain information about the stresses present in the chemically strengthened glass cover member  852 . In some cases, light from the polarization analyzer may form a photoelastic pattern, such as an isochromic pattern alone or in combination with an isoclinic pattern. Light from the photoelastic pattern may be detected to form an image of the chemically strengthened glass cover member  852 . 
     The photoelastic pattern may be an interference pattern. When the polarized light is directed onto the chemically strengthened glass cover member in a direction parallel to its thickness, the resulting interference pattern may contain information about membrane stresses in the chemically strengthened glass cover member. Two dimensional photoelasticity methods may be used to analyze these membrane stresses (also referred to herein as area stresses) as will be described in more detail with respect to  FIG.  9   . 
     The sensor  887  may be any of a variety of devices used to detect light. For example, the sensor  887  may be a semiconductor device such as a photodiode. The sensor may be an image sensor such a charge-coupled device (CCD) sensor or a complementary metal-oxide semiconductor (CMOS) sensor. The sensor  887  may also be referred to as a detector herein. The sensor  887  may be configured to produce an electrical output which corresponds to an intensity or a color value (e.g., a red, green, or blue value) of the light received at a given location of the sensor (e.g., at a given pixel of the sensor). In some cases, the sensor  887  and the polarization analyzer  885  may be combined in a system component such as a polariscope or a strain viewer. 
     Optical systems suitable for use with the methods described herein may include elements in addition to the optical elements shown in  FIG.  8   . For example, such an optical system may include one or more of a compensator, a quarter wave plate, or a full wave plate. In addition, optical systems may include a computing device and/or other devices which support automation of photoelastic measurements. 
       FIG.  9    schematically shows an example of an image  900  of a chemically strengthened glass cover member. The image  900  may be a photoelastic image containing information about the stresses present in the chemically strengthened glass cover member. The chemically strengthened glass cover member may be an example of glass cover members  152 ,  252 ,  352 , or any other glass cover members described herein and, for brevity, the description of these glass cover members is not repeated here. 
     In the example of  FIG.  9   , the image  900  is a grayscale image that includes different lightness values. The differences in lightness values are schematically shown in  FIG.  9    with stippling, with a greater density of dots corresponding to a reduced lightness value. The differences in lightness values create contrast between different regions of the image. In some cases, the lightness value of a given region of the image relates to the intensity of the light received by a device used to detect the photoelastic pattern. The optical measurement provided by the sensor may therefore be an intensity measurement. In additional embodiments, the image  900  may be a color image and the optical measurement(s) provided by the sensor may be one or more color values. As previously discussed with respect to  FIG.  8   , the sensor may provide an electrical output corresponding to the optical measurement. 
     The first region  956  of the image  900  may have a first lightness value. The first region  956  may correspond to a first portion of the glass cover member which at least partially defines a curved boundary of an opening in the glass cover member (as previously described with respect to  FIGS.  2 - 4   ). A second region  958  of the image  900  may have a second lightness value different than the first lightness value. The second region  958  of the image may correspond to a second portion of the glass cover member located away from the opening. In some cases, the distance between the second portion of the glass cover member and the opening is greater than or equal to a thickness of the chemically strengthened glass cover member. 
     In some embodiments, the difference between the first lightness value of the first region  956  of the image and the second lightness value of the second region  958  of the image can be used as a quality control check for a level of chemical strengthening of the glass cover member. For example, the measured difference between the first and second lightness values can be compared to a target range for the difference between the first and the second lightness values. When the measured difference between the first and second lightness values exceeds this target range, the level of chemical strengthening may be higher than desired. Similarly, when the measured difference between the first and second lightness values is below this target range, the level of chemical strengthening may be lower than desired. 
     In some embodiments, the first lightness value of the first region  956  of the image or the difference between the first lightness value of the first region  956  and the second lightness value of the second region  958  of the image can be used to estimate a localized stress level in a first portion of the glass cover member. In general, the intensity value of a region of the photoelastic image is related to the difference in principal stresses of a corresponding portion of the glass cover member, as is explained in further detail below. In some embodiments, a localized stress level may be estimated by determining the difference in principal stresses σ 1 −σ 2  in a given portion of the glass cover member. When the given portion of the glass cover member is at an edge or side surface (including at the edge or boundary of an opening), one of the principal stresses may be zero and a localized stress level may be estimated by determining the value of the non-zero principal stress. In some cases, the value of the non-zero principal stress may provide an estimate of an edge stress value at the edge or side surface. In additional cases, the localized stress value of a region of the image can be estimated when the region is at the center of a light fringe or a dark fringe. 
     If the localized stress level in a first portion of the glass cover member is known, the localized stress level in the second portion of the glass cover member can be estimated in several ways. For example, when the first portion is located near an opening or other geometric feature in the glass cover member and the second portion is located away from the opening, the localized stress level in the first portion may be equal to a localized stress level in the second portion times a stress multiplier value. The localized stress level in the second portion may therefore be estimated as the localized stress level in the first portion divided by the stress multiplier value. The localized stress level in the second portion may also be estimated by comparing the second lightness value to a lightness value of a reference chemically strengthened glass cover member having a known localized stress level. 
     In some embodiments, the first lightness value of the first region  956  of the image or the difference between the first lightness value of the first region  956  and the second lightness value of the second region  958  of the image can be used to estimate a localized stress level in a first portion of the glass cover member. The description provided herein with respect to lightness values of a given region of the image may also be applicable to one or more color values of a given region of the image. 
     In general, the intensity value of a region of the photoelastic image is related to the difference in principal stresses of a corresponding portion of the glass cover member. The intensity at any given region of the photoelastic image can be related to a phase difference Δ of the interfering light. The relationship between the phase difference Δ and the intensity may depend upon the measurement technique used (e.g. whether a dark-field or a light-field technique is used). The phase difference Δ may be related to a retardation value δ by the relationship Δ=2πδ/λ, where λ is the wavelength of light. The retardation value δ may also be referred to herein as a fringe order. The retardation value δ gives at least some information about the stress in the chemically strengthened glass cover member. For example, the difference in principal stresses σ 1 −σ 2  may be equal to δ/(CD), where C is a photoelastic constant and D is a thickness of the chemically strengthened glass cover member. 
     The retardation value or phase difference of a region of the image can be determined in several ways. In some cases, the retardation value for a pixel of the image can be determined by comparing an intensity value or one or more color values of the pixel to a set of calibration values for the system. The set of calibration values may be in the form of a scale or a table such as a look-up table. For example, for RGB photoelasticity using a white light source and a RGB detector, the retardation for a given pixel can be determined by comparing its color values (e.g., the red (R), green (G), and blue (B) values) to values in the calibration table or look-up table. The comparison may be an automated comparison. In additional cases, the phase difference or retardation value can be determined by analyzing the variation in the signal from a pixel of the image for multiple positions of the analyzer (e.g., when the analyzer is rotated). In a dark-field isochromic pattern the centers of dark fringes are integral values of the retardation value δ and in a light-field isochromic pattern the centers of light fringes are integral values of the retardation value δ. 
     The stresses in the glass cover member can also be determined in several ways. In some cases, the stresses can be determined from retardation values or phase difference values, alone or in combination with additional information. For example, the stresses may be determined numerically based on the retardation values or phase difference values. In additional cases, an intensity value of a given region of the image may be referenced to a reference (e.g., background) value and this referenced intensity value may be used to estimate a localized stress value of a portion of the chemically strengthened glass cover member. For example, the difference between the first lightness value of the first region  956  of the image and the second lightness value of the second region  958  of the image may be used to provide a referenced intensity value (also referred to as a relative intensity value). The referenced intensity value may be used to estimate a localized stress value of the first portion of the chemically strengthened glass cover member. If the first region  956  is at the center of a light fringe or a dark fringe, a retardation value δ of the first region  956  can be determined from the interference pattern and used to estimate a localized stress level in a first portion of the glass cover member. 
     In some cases, the optical anisotropy or iridescence of a portion of the cover member can also be predicted from the retardation value or the phase difference. The methods disclosed herein can therefore also be used to predict whether the optical anisotropy of the cover member will be unacceptably high under particular viewing conditions. 
       FIG.  10    shows a flow chart of a process  1000  for evaluating a chemically strengthened glass component of an electronic device. For example, the process  1000  may allow estimation of a level of chemical strengthening of the glass component. The glass component may be a glass cover member. The glass component may be an example of glass cover members  152 ,  252 ,  352 , or any other glass cover members described herein and, for brevity, the description of these glass cover members is not repeated here. The process  1000  may also be applicable to other types of chemically strengthened transparent components as described herein. 
     An operation  1002  of the process  1000  comprises directing polarized light through the glass component. The polarized light may be produced by a light source in combination with a polarizer. The polarizer may be a linear polarizer having a first polarization axis. Alternately, the polarizer may produce elliptically polarized or circularly polarized light. For example, a polarizer configured to produce elliptically polarized or circularly polarized light may include a linear polarizer and a quarter wave plate. In some cases, a lens or other optical element may be placed between the polarizer and the chemically strengthened glass component. The light source may produce monochromatic light or light covering a wider spectrum, such as the visible spectrum of light. Additional description of light sources is provided with respect to  FIG.  8    and that description is generally applicable herein. 
     The operation  1002  of the process  1000  further comprises directing the polarized light through a polarization analyzer after it emerges from the glass component. As previously discussed with respect to  FIG.  8   , the polarization analyzer may include a polarizer. When the polarized light is produced by a light source in combination with a first polarizer, the polarization analyzer may include a second polarizer. The first polarizer may have a first orientation and the second linear polarizer may have a second orientation different from the first orientation (and not equivalent to the first orientation). For example, when the first and the second polarizers are linear polarizers the second polarization may be rotated with respect to the first orientation by an angle greater than zero degrees and less than 180 degrees. Additional description of polarization analyzers is provided with respect to  FIG.  8    and that description is generally applicable herein. The operation of the polarization analyzer may be automated and measurements may be performed at multiple positions of the analyzer. 
     The operation  1002  of the process  1000  further comprises directing the polarized light onto a sensor after it emerges from the polarization analyzer. The sensor may be used to detect light and produce at least one optical measurement. The light may be detected with an image sensor, such as a charge-coupled device (CCD) sensor or a complementary metal-oxide semiconductor (CMOS) sensor. Additional description of sensors is provided with respect to  FIG.  8    and that description is generally applicable herein. 
     An operation  1004  of the process  1000  comprises determining a differential intensity value from at least one optical measurement of a first portion and a second portion of the glass component. For example, the operation  1004  may comprise determining a first intensity value corresponding to the first portion and a second intensity value corresponding to the second portion. The operation  1004  may further comprise determining a difference between the first intensity value and the second intensity value. The first portion of the glass component may be located near an opening or other geometric feature in the glass component (e.g., portion  357  of  FIG.  3   ). For example, the first portion of the glass component may at least partially define a curved boundary of an opening in the glass component. The second portion of the glass component may be located away from the geometric feature in the glass component (e.g., portion  358  of  FIG.  3   ). 
     An operation  1006  of the process  1000  comprises estimating a localized stress level of the first portion based on the differential intensity value. The localized stress level of the first portion may be estimated as described with respect to  FIG.  9    and, for brevity, that discussion is not repeated here. 
     An operation  1008  of the process  1000  comprises determining a stress multiplier value. The stress multiplier value is typically estimated based on the shape of the geometric feature. When the geometric feature is an opening, the stress multiplier may be based on a curvature of a boundary defining the opening (e.g., a maximum curvature). As an example, the stress multiplier value may be estimated based on a finite element calculation of the residual stress in the chemically strengthened glass component. As an additional example, the stress multiplier value may be estimated based on previously measured or calculated stress concentration values for comparable stress loadings and opening shapes. The stress multiplier value may be estimated similarly when the geometric feature is a projection or other feature which may lead to a concentration of residual stress. 
     The operation  1008  may further include an operation of obtaining an estimate of the curvature of the curved boundary. In some cases, the curvature may be obtained based on a specified curvature of the curved boundary (e.g., a product specification for the glass component). In other cases, the curvature of the part may be measured, such as with a measuring microscope or using a machine vision technique as described with respect to optical inspection unit  1210  of system  1200 . 
     An operation  1010  of the process  1000  comprises estimating a chemical strengthening level of the glass component. In some cases, the operation of estimating the chemical strengthening level may be based on the localized stress level (of the first portion) and the stress multiplier value. For example, the chemical strengthening level of the glass component may be estimated by estimating a compressive surface stress of a compressive stress region or layer. In addition, the chemical strengthening level of the glass component may be estimated by estimating a depth of a compressive stress region or layer. For example, the depth of the compressive stress region may be estimated based on an estimate of the compressive surface stress and a predicted relationship between stress and distance into the part (e.g., along the thickness). The predicted relationship between stress and thickness may be at least partially based on an experimental measurement of stress as a function of thickness for one or more reference samples. As an additional example, the depth of the compressive stress region or other measure of the chemical strengthening level may be based on a correlation between one or more of the localized stress levels estimated in operation  1006  and the chemical strengthening level. 
     The process  1000  may further comprise one or more operations. For example, the process  1000  may further comprise an operation of comparing the first localized stress level to a reference stress range. In addition, the process  1000  may further comprise comparing the chemical strengthening level of the glass component to a reference chemical strengthening range. Further, the process  1000  may comprise an operation of estimating a second localized stress level at the second portion of the glass component. In addition, when an operation of comparing indicates that a localized stress level or chemical strengthening level is outside a target range the glass component may be rejected and/or discarded. 
       FIG.  11    shows another example of a process  1100  for evaluating a chemically strengthened glass component of an electronic device. Process  1100  may allow estimation of a stress level in the chemically strengthened glass component. As previously described, the glass component may be a glass cover member. The chemically strengthened glass component may be an example of glass cover members  152 ,  252 ,  352 , or any other glass cover members described herein and, for brevity, the description of these glass cover members is not repeated here. Process  1100  may also be applicable to other types of chemically strengthened transparent components as described herein. 
     An operation  1102  of process  1100  comprises forming an interference pattern. The operation  1102  comprises passing polarized light through a chemically strengthened glass component and through a polarization analyzer. These steps of operation  1102  may be similar to the steps of directing the polarized light through the glass component and through the polarization analyzer of the operation  1002  of the process  1000  and, for brevity, the details of the operation  1002  are not repeated here. 
     An operation  1104  of the process  1100  comprises receiving the interference pattern at a light sensor. The sensor may be similar to the sensors described with respect to  FIGS.  8  and  10    and, for brevity, those details are not repeated here. 
     An operation  1106  of process  1100  comprises analyzing the interference pattern. As shown in  FIG.  11   , the operation  1106  comprises determining an intensity value corresponding to a first portion of the glass component. The first portion of the glass component may be located near an opening or other geometric feature in the glass component. For example, the first portion may at least partially define a curved boundary of an opening in the glass component. The operation  1106  further comprises estimating a first localized stress level of the first portion, which may be based on the intensity value. These steps of the operation  1106  may be similar to the steps of determining the intensity values and the first localized stress level previously described with respect to the operations  1004  and  1006  of the process  1000  and, for brevity, the details are not repeated here. 
     The operation  1106  further comprises estimating a stress multiplier value for the first portion of the glass component. In some cases, estimation of the stress multiplier value is based on a curvature of the curved boundary of the opening in the glass component. This portion of the operation  1106  may be similar to that previously described with respect to the operation  1008  of the process  1000  and, for brevity, the details are not repeated here. Optionally the operation  1106  further comprises measuring the curvature of the curved boundary. The curvature may be measured with an optical inspection unit as described with respect to  FIG.  12    or by other optical measurement techniques. 
     The operation  1106  further comprises estimating a second localized stress level of a second portion of the chemically strengthened glass component. The estimation of the second localized stress level may be based on the first localized stress level and a stress multiplier value. The second portion may be located away from the opening in the glass component. In some cases the second localized stress level may be estimated as the first localized stress level divided by the stress multiplier value as previously discussed with respect to  FIG.  9   . 
     In additional cases, the operation  1106  of analyzing the interference pattern may comprise an alternate sequence of operations. For example, the operation  1106  may comprise determining a first intensity value corresponding to the first portion of the chemically strengthened glass component and a second intensity value corresponding to a second portion of the chemically strengthened glass component, determining respective retardation values of the first and the second portions based on these intensity values, and determining localized stress levels of the first and the second portions based on these retardation values by any of the applicable procedures previously described with respect to  FIG.  9   . The description provided with respect to  FIG.  9    is generally applicable herein and, for brevity, is not repeated here. 
     As previously described for process  1000 , process  1100  may further comprise one or more operations. For example, the process  1100  may further comprise an operation of comparing the first localized stress level and/or the second localized stress level to a reference stress range. As another example, the process  1100  may further comprise an operation of estimating a chemical strengthening level of the glass component based on the first localized stress level, the second localized stress level, or a combination thereof. In addition, the process  1100  may further comprise comparing the chemical strengthening level of the glass component to a reference chemical strengthening range. Further, when an operation of comparing indicates that a localized stress level or chemical strengthening level is outside a target range the glass component may be rejected and/or discarded. 
       FIG.  12    schematically shows a system  1200  for evaluating a chemically strengthened glass component such as a glass cover member. The system  1200  may be configured to measure an opening or other geometric feature in the glass component. The system  1200  may also be configured to analyze the residual stresses in the glass component resulting from the chemical strengthening process. As shown in  FIG.  12   , the system  1200  comprises a first optical inspection unit  1210 , a second optical inspection unit  1220 , a transport device  1230 , and a computing device  1240 . 
     The first optical inspection unit  1210  may be configured to measure an opening in the chemically strengthened glass component. In particular, the optical inspection unit  1210  may be configured to measure a curvature of a boundary of the opening in the glass component. The curvature may be measured or estimated using machine vision. For example, the curvature may be measured or estimated using edge detection and/or edge analysis conducted over the respective region of the image. The first optical inspection unit may be an automated optical inspection unit (AOI). An automated optical inspection unit may also be referred to herein as an automatic visual inspection unit. In some cases the first inspection unit  1210  or another component of the system  1200  is configured to measure a thickness of the glass component. 
     The first optical inspection unit  1210  may include a first light source and a first image acquisition device. The first light source may be any light source suitable for determining the dimensions of the opening in the chemically strengthened glass component. The first image acquisition device may include an image sensor, such as a charge-coupled device (CCD) sensor or a complementary metal-oxide semiconductor (CMOS) sensor. The first optical inspection unit  1210  may also include a first processor. The first optical inspection unit  1210  may be configured to receive input from the image sensor and to determine a curvature value and optionally other dimensions of the opening in the glass component using the first processor. 
     The second optical inspection unit  1220  may be configured to obtain at least one optical measurement of the chemically strengthened glass component which is suitable for analyzing the residual stress in one or more portions of the glass component resulting from the chemical strengthening process. The second optical inspection unit  1220  may be configured to obtain an image of the chemically strengthened glass component. The second optical inspection unit  1220  may include a second light source, a polarizer, an analyzer, and a second image acquisition device. The second optical inspection unit  1220  may also include a second processor. In some cases, the computing device  1240  may be configured to receive the input from the second image acquisition device and to determine the residual stress(es). The second optical inspection unit may be an automated optical inspection unit. 
     The second light source may produce monochromatic light or light covering a wider spectrum, such as over the visible spectrum of light. The polarizer, in combination with the second light source, produces polarized light. The polarizer may be a linear polarizer having a first polarization axis. Alternately, the polarizer may produce elliptically polarized or circularly polarized light. For example, a polarizer configured to produce elliptically polarized or circularly polarized light may include a linear polarizer and a quarter wave plates. 
     The analyzer may be configured to produce an interference pattern by combining polarization components of the light emerging from the chemically strengthened glass component. For example, the analyzer may be configured to act as a second polarizer. In some cases, the analyzer may include a second linear polarizer having a second polarization axis. Typically the second polarization axis is rotated with respect to the first polarization axis and may be at about ninety degrees with respect to the first polarization axis. As an additional example, the analyzer may include a second linear polarizer and a second quarter wave plate. 
     The second image acquisition device may be similar to the first image acquisition device and for brevity that description is not repeated here. In some cases the second image acquisition device is color image acquisition device such as a 3CCC, a tri-linear, or a Bayer pattern camera. The second processor of the second optical inspection unit may be configured to determine the intensity values (or lightness values) at various regions of the image. 
     In some embodiments, the first optical inspection unit  1210  and the second optical inspection unit  1220  share components. As an example, the first image sensor and the second image sensor may share components. Further, the first processor and the second processor may share components. In additional embodiments, the first image sensor and the second image sensor are different from one another. The first processor and the second processor may also be different from one another. 
     As shown in  FIG.  12   , the system  1200  further comprises a transport device  1230 . Inclusion of a transport device  1230  in the system  1200  may be optional, such as when the first optical inspection unit  1210  and the second optical inspection unit  1220  share components. 
     The transport device may be any such device known to the art capable of transporting the chemically strengthened glass component without scratching or otherwise damaging it. The transport device  1230  is configured to deliver the glass component from the first optical inspection unit to the second optical inspection unit. In addition, the transport device  1230  may be further configured to discard the glass component when receiving a signal from the computing system  1240 , as discussed in further detail below. 
     The system  1200  further comprises a computing device  1240 . As shown in  FIG.  12   , the computing device  1240  is in communication with the first optical inspection unit and the second optical inspection unit. The computing device  1240  may comprise a memory containing instructions and a third processor configured to execute the instructions and thereby cause the computing system to perform operations. 
     The operations may include receiving the curvature value from the first optical inspection unit and estimating a stress multiplier value based on the curvature value. The operations may further include estimating a first localized stress level in the first portion of the glass component based on a difference between the first intensity value and the second intensity value. The operations may further include estimating a chemical strengthening level of the glass component based on the localized stress level and the stress multiplier value. In addition, the operations may include estimating a second localized stress level in the second portion of the glass component. The estimation of the second localized stress level may be based on the first localized stress level and the stress multiplier value. 
     In addition, the third processor may be configured to cause the computing system to compare the first localized stress level and the second localized stress level to the reference stress range and/or to compare the chemical strengthening level to a reference chemical strengthening range. The third processor may be configured to cause the computing system to provide a signal when the first localized stress level and/or the second localized stress level is outside the reference stress range. The third processor may also be configured to provide a signal when the chemical strengthening level is outside the reference chemical strengthening range. The system may be configured to respond to the signal by discarding the glass component. For example, the signal may be provided to the transport system and the transport system may respond by discarding the glass component. 
     The foregoing description provides an example of a system for estimating a stress level in a glass component such as a glass cover member. Modifications and variations of system  1200  are also within the scope of the disclosure herein. For example, a system may also be configured to perform the operations of the method described in  FIG.  11    or of any other method described herein. 
       FIG.  13    shows a block diagram of a sample electronic device that can incorporate a transparent component as described herein. The schematic representation depicted in  FIG.  13    may correspond to components of the devices depicted in  FIG.  1 A- 12    as described above. However,  FIG.  13    may also more generally represent other types of electronic devices with cover assemblies as described herein. 
     In embodiments, an electronic device  1300  may include sensors  1320  to provide information regarding configuration and/or orientation of the electronic device in order to control the output of the display. For example, a portion of the display  1308  may be turned off, disabled, or put in a low energy state when all or part of the viewable area of the display  1308  is blocked or substantially obscured. As another example, the display  1308  may be adapted to rotate the display of graphical output based on changes in orientation of the device  1300  (e.g., 90 degrees or 180 degrees) in response to the device  1300  being rotated. 
     The electronic device  1300  also includes a processor  1306  operably connected with a computer-readable memory  1302 . The processor  1306  may be operatively connected to the memory  1302  component via an electronic bus or bridge. The processor  1306  may be implemented as one or more computer processors or microcontrollers configured to perform operations in response to computer-readable instructions. The processor  1306  may include a central processing unit (CPU) of the device  1300 . Additionally, and/or alternatively, the processor  1306  may include other electronic circuitry within the device  1300  including application specific integrated chips (ASIC) and other microcontroller devices. The processor  1306  may be configured to perform functionality described in the examples above. 
     The memory  1302  may include a variety of types of non-transitory computer-readable storage media, including, for example, read access memory (RAM), read-only memory (ROM), erasable programmable memory (e.g., EPROM and EEPROM), or flash memory. The memory  1302  is configured to store computer-readable instructions, sensor values, and other persistent software elements. 
     The electronic device  1300  may include control circuitry  1310 . The control circuitry  1310  may be implemented in a single control unit and not necessarily as distinct electrical circuit elements. As used herein, “control unit” will be used synonymously with “control circuitry.” The control circuitry  1310  may receive signals from the processor  1306  or from other elements of the electronic device  1300 . 
     As shown in  FIG.  13   , the electronic device  1300  includes a battery  1314  that is configured to provide electrical power to the components of the electronic device  1300 . The battery  1314  may include one or more power storage cells that are linked together to provide an internal supply of electrical power. The battery  1314  may be operatively coupled to power management circuitry that is configured to provide appropriate voltage and power levels for individual components or groups of components within the electronic device  1300 . The battery  1314 , via power management circuitry, may be configured to receive power from an external source, such as an alternating current power outlet. The battery  1314  may store received power so that the electronic device  1300  may operate without connection to an external power source for an extended period of time, which may range from several hours to several days. 
     In some embodiments, the electronic device  1300  includes one or more input devices  1318 . The input device  1318  is a device that is configured to receive input from a user or the environment. The input device  1318  may include, for example, a push button, a touch-activated button, capacitive touch sensor, a touch screen (e.g., a touch-sensitive display or a force-sensitive display), capacitive touch button, dial, crown, or the like. In some embodiments, the input device  1318  may provide a dedicated or primary function, including, for example, a power button, volume buttons, home buttons, scroll wheels, and camera buttons. 
     The device  1300  may also include one or more sensors  1320 , such as a force sensor, a capacitive sensor, an accelerometer, a barometer, a gyroscope, a proximity sensor, a light sensor, or the like. The sensors  1320  may be operably coupled to processing circuitry. In some embodiments, the sensors  1320  may detect deformation and/or changes in configuration of the electronic device and be operably coupled to processing circuitry which controls the display based on the sensor signals. In some implementations, output from the sensors  1320  is used to reconfigure the display output to correspond to an orientation or folded/unfolded configuration or state of the device. Example sensors  1320  for this purpose include accelerometers, gyroscopes, magnetometers, and other similar types of position/orientation sensing devices. In addition, the sensors  1320  may include a microphone, acoustic sensor, light sensor, optical facial recognition sensor, or other types of sensing device. 
     In some embodiments, the electronic device  1300  includes one or more output devices  1304  configured to provide output to a user. The output device  1304  may include display  1308  that renders visual information generated by the processor  1306 . The output device  1304  may also include one or more speakers to provide audio output. The output device  1304  may also include one or more haptic devices that are configured to produce a haptic or tactile output along an exterior surface of the device  1300 . 
     The display  1308  may include a liquid-crystal display (LCD), light-emitting diode (LED) display, an LED-backlit LCD display, organic light-emitting diode (OLED) display, an active layer organic light-emitting diode (AMOLED) display, organic electroluminescent (EL) display, electrophoretic ink display, or the like. If the display  1308  is a liquid-crystal display or an electrophoretic ink display, the display  1308  may also include a backlight component that can be controlled to provide variable levels of display brightness. If the display  1308  is an organic light-emitting diode or organic electroluminescent-type display, the brightness of the display  1308  may be controlled by modifying the electrical signals that are provided to display elements. In addition, information regarding configuration and/or orientation of the electronic device may be used to control the output of the display as described with respect to input devices  1318 . In some cases, the display is integrated with a touch and/or force sensor in order to detect touches and/or forces applied along an exterior surface of the device  1300 . 
     The electronic device  1300  may also include a communication port  1312  that is configured to transmit and/or receive signals or electrical communication from an external or separate device. The communication port  1312  may be configured to couple to an external device via a cable, adaptor, or other type of electrical connector. In some embodiments, the communication port  1312  may be used to couple the electronic device to a host computer. 
     The electronic device  1300  may also include at least one accessory  1316 , such as a camera, a flash for the camera, or other such device. The camera may be included in a camera assembly. The camera may be connected to other parts of the electronic device  1300  such as the control circuitry  1310 . 
     As used herein, use of the term “about” in reference to the endpoint of a range may signify a variation of +/−5%, +/−2%, or +/−1% of the endpoint value. In addition, disclosure of a range in which at least one endpoint is described as being “about” a specified value includes disclosure of the range in which the endpoint is equal to the specified value. 
     The following discussion applies to the electronic devices described herein to the extent that these devices may be used to obtain personally identifiable information data. It is well understood that the use of personally identifiable information should follow privacy policies and practices that are generally recognized as meeting or exceeding industry or governmental requirements for maintaining the privacy of users. In particular, personally identifiable information data should be managed and handled so as to minimize risks of unintentional or unauthorized access or use, and the nature of authorized use should be clearly indicated to users. 
     The foregoing description, for purposes of explanation, used specific nomenclature to provide a thorough understanding of the described embodiments. However, it will be apparent to one skilled in the art that the specific details are not required in order to practice the described embodiments. Thus, the foregoing descriptions of the specific embodiments described herein are presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the embodiments to the precise forms disclosed. It will be apparent to one of ordinary skill in the art that many modifications and variations are possible in view of the above teachings.

Metadata:
Filing Date: 20200617
Publication Date: 20230620
Grant Date: 20230620
Priority Date: 20190709
Inventors: MARSHALL, TYLER A.
BARTLOW, CHRISTOPHER C.
Assignee: APPLE INC
CPC Classifications: [{"code": "G01N21/21", "inventive": true, "first": false, "tree": "[]"}, {"code": "C03C17/30", "inventive": true, "first": true, "tree": "[]"}, {"code": "B44C1/00", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01N21/21", "inventive": true, "first": false, "tree": "[]"}, {"code": "C03C17/30", "inventive": true, "first": true, "tree": "[]"}, {"code": "B44C1/00", "inventive": true, "first": false, "tree": "[]"}, {"code": "C03C17/30", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01N21/23", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 74101883