Evaluation of transparent components for electronic devices

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.