Structured illumination optical inspection platform for transparent materials

Patent metadata

Field	Value
Publication number	US-11226293-B1
Application number	US-202016988435-A
Country	US
Kind code	B1
Filing date	Aug 7, 2020
Priority date	Aug 7, 2020
Publication date	Jan 18, 2022
Grant date	Jan 18, 2022

Abstract

A method of imaging surface features with a large (non-microscopic) field-of-view includes projecting a structured illumination pattern onto the transparent target. The surface features modify the structured illumination pattern, and an image of the modified structured illumination pattern is imaged at each of multiple different introduced phase shifts via an imaging device. The method further provides for extracting, from each of the captured phase-shifted images, image components that correspond to frequencies exceeding a cutoff frequency of the imaging device; and using the extracted image components to construct a corrected image of the surface features of the transparent target. The corrected image has a resolution that is greater than a spatially incoherent point-to-point optical resolution of the imaging device.

First claim

What is claimed is:

1. A method comprising:
projecting a structured illumination pattern onto a transparent target, the transparent target including surface features that modify the structured illumination pattern;
capturing, with an imaging device, an image of the modified structured illumination pattern at each of multiple different introduced phase shifts;
extracting, from the captured images, image components that correspond to frequencies exceeding a cutoff frequency of the imaging device; and
constructing a corrected image of the surface features of the transparent target based on the extracted image components, the corrected image having a resolution that is greater than a spatially incoherent point-to-point optical resolution of the imaging device.

2. The method of claim 1 , further comprising: wherein projecting the structured illumination further comprises:
projecting light sequentially through a grayscale photomask and through a first side of the transparent target.

3. The method of claim 2 , wherein the grayscale photomask has a sinusoidal pattern with a pitch equal to a cutoff frequency of the imaging device.

4. The method of claim 2 , wherein the method further comprises:
capturing an image of the projected structured illumination at each of the multiple different positions of the grayscale photomask.

5. The method of claim 2 , wherein the phase shifts are introduced by moving the photomask along a motorized stage.

6. The method of claim 1 , wherein the structured illumination is projected onto a first side of the transparent target and the method further comprises:
imaging the structured illumination on a second opposite side of the transparent target.

7. The method of claim 1 , wherein extracting the image components that correspond to frequencies in excess of the cutoff frequency of the imaging device further comprises:
converting each of the captured images to an associated frequency domain representation; and
extracting the image components from the frequency domain representations of the images.

8. The method of claim 1 , further comprising:
shifting of each of the extracted image components in a frequency domain using a 2D Fourier domain interpolation shifting scheme.

9. The method of claim 8 , wherein constructing the corrected image further comprises:
combining the shifted extracted image components to generate the corrected image.

10. A system comprising:
a light source positioned to project light onto a wavefront modulator to generate a structured illumination;
a transparent target positioned to receive the structured illumination, the transparent target including surface features that modify the structured illumination;
an imaging device positioned to capture an image of the modified structured illumination at each of multiple different introduced phase shifts;
an image processor configured to:
extract, from the captured images, image components that correspond to frequencies exceeding a cutoff frequency of the imaging device; and
creating a corrected image of the surface features of the transparent target based on the extracted image components, the corrected image having a resolution that is greater than a spatially incoherent point-to-point optical resolution of the imaging device.

11. The system of claim 10 , wherein the image processor is further executable to:
convert each of the captured images to an associated frequency domain representation; and
extract the image components from the frequency domain representations of the images.

12. The system of claim 10 , wherein the wavefront modulator is a grayscale photomask.

13. The system of claim 12 , wherein the grayscale photomask has a sinusoidal pattern with a pitch equal to a cutoff frequency of the imaging device.

14. The system of claim 10 , further comprising:
a motorized stage that moves the wavefront modulator across a range of positions.

15. The system of claim 10 , wherein the imaging device includes a telecentric lens.

16. The system of claim 10 , wherein each of the multiple different introduced phase shifts has a magnitude equal to the cutoff frequency of the imaging device.

17. A system comprising:
a grayscale photomask adapted to project a structured illumination;
a light source positioned to project light onto the grayscale photomask to generate a structured illumination;
a transparent target positioned to receive the structured illumination, the transparent target including surface features that modify the structured illumination;
an imaging device positioned to capture an image of the modified structured illumination pattern at each of multiple different phase shift of the structured illumination; and
an image processor configured to generate a corrected image of the surface features using the captured images, the corrected image having a resolution greater than a spatially incoherent point-to-point optical resolution of the imaging device.

18. The system of claim 17 , wherein the grayscale photomask has a pattern pitch equal to a cutoff frequency of the imaging device.

19. The system of claim 17 , further comprising:
a motorized stage that moves the grayscale photomask across a range of positions.

20. The system of claim 17 , wherein the imaging device includes a telecentric lens.

Assignees

• Seagate Technology Llc

Inventors

• Feng Kaijun

Classifications

• G01N21/958

  Inspecting transparent materials {or objects, e.g. windscreens (for conveyed flat sheet or rod G01N21/896)} · CPC title

• G06T7/0004

  Industrial image inspection · CPC title

• G06T5/50

  using two or more images, e.g. averaging or subtraction · CPC title

• G01M11/081

  by using a contact-less detection method, i.e. with a camera · CPC title

• G06T2207/10152

  Varying illumination · CPC title