Method for measuring surface characteristics in optically distorting media

Patent metadata

Field	Value
Publication number	US-12228392-B2
Application number	US-202318487091-A
Country	US
Kind code	B2
Filing date	Oct 15, 2023
Priority date	Oct 12, 2018
Publication date	Feb 18, 2025
Grant date	Feb 18, 2025

Abstract

Provided is a method for measuring surface characteristics of at least a portion of an object, including providing a light source; generating a first interference pattern on the at least a portion of the object; capturing an image of the first interference pattern; shifting the phase of the light source to generate a second interference pattern; capturing an image of the second interference pattern; filtering distortion from the interference patterns; extracting a wrapped phase of the at least a portion of the object based on the images; unwrapping the wrapped phase of the at least a portion of the object to generate an unwrapped phase; identifying a computed depth map distance to the at least a portion of the object; and fitting an ideal part to the computed depth map of the at least a portion of the object to measure the surface characteristics.

First claim

What is claimed is:

1. A method for measuring surface characteristics of at least a portion of an object comprising:
providing at least one light source;
directing light from the at least one light source to generate a first interference pattern on the at least a portion of the object;
capturing at least one first image of the first interference pattern;
shifting the phase of the at least one light source to generate a second interference pattern;
capturing at least one second image of the second interference pattern;
filtering distortion from the first interference pattern and/or the second interference pattern;
extracting a wrapped phase of the at least a portion of the object based on the at least one first image and the at least one second image;
unwrapping the wrapped phase of the at least a portion of the object to generate an unwrapped phase;
identifying a computed depth map distance to the at least a portion of the object based on the unwrapped phase; and
fitting an ideal part to the computed depth map of the at least a portion of the object to measure the surface characteristics,
wherein the object is at least partially submerged in an optically distorting liquid medium of variable and changing indexes of refraction, and
wherein the object is substantially cylindrical, substantially spherical, or substantially flat on at least one surface, and wherein said measuring surface characteristics includes determining a thickness change of at least a portion of an object.

2. The method of claim 1 , wherein the first interference pattern and/or second interference pattern is generated by directing the light through a grating, viewing light from the at least one light source through a mask, or combining the light with a reference beam.

3. The method of claim 2 , wherein said method comprises, in order:
providing at least one light source;
directing light from the light source through a grating and onto the object to generate a first interference pattern on the at least a portion of the object;
capturing at least one first image of the first interference pattern;
shifting the phase of the at least one light source to generate a second interference pattern;
capturing at least one second image of the second interference pattern;
filtering distortion from the first interference pattern and/or the second interference pattern;
extracting a wrapped phase of the at least a portion of the object based on the at least one first image and the at least one second image;
unwrapping the wrapped phase of the at least a portion of the object;
identifying a computed depth map distance to the at least a portion of the object based on the wrapped phase; and
fitting an ideal part to the computed depth map of the at least a portion of the object to measure the surface characteristics.

4. The method of claim 1 , wherein the optically distorting liquid medium comprises water.

5. The method of claim 1 , wherein the object is substantially cylindrical.

6. The method of claim 5 , wherein the object is at least one nuclear fuel rod or steam generator tube or conduit.

7. The method of claim 6 , wherein the at least one light source is a laser, optionally a multi-line laser, and said directing light comprises projecting a laser fringe of adjustable phase through a volume containing the object.

8. The method of claim 3 , wherein the grating and the object define a distance d therebetween, wherein d is at least a minimum distance required for safety considerations involving nuclear fuel.

9. The method of claim 1 , wherein said capturing the at least one first image of the first interference pattern and/or the at least one second image of the second interference pattern comprises gathering light from the at least a portion of an object with a telecentric lens and directing the image to an imaging sensor.

10. A method for measuring surface characteristics of at least a portion of an object comprising:
providing at least one light source;
directing light from the at least one light source to generate a first interference pattern on the at least a portion of the object;
capturing at least one first image of the first interference pattern;
shifting the phase of the at least one light source to generate a second interference pattern;
capturing at least one second image of the second interference pattern;
filtering distortion from the first interference pattern and/or the second interference pattern;
extracting a wrapped phase of the at least a portion of the object based on the at least one first image and the at least one second image;
unwrapping the wrapped phase of the at least a portion of the object to generate an unwrapped phase;
identifying a computed depth map distance to the at least a portion of the object based on the unwrapped phase; and
fitting an ideal part to the computed depth map of the at least a portion of the object to measure the surface characteristics,
wherein the object is at least partially submerged in an optically distorting liquid medium of variable and changing indexes of refraction, including at least one of the following:
(a) said capturing the at least one first image of the first interference pattern and/or the at least one second image of the second interference pattern utilizes a filter configured to substantially block ambient light; and/or
(b) the first interference pattern and/or the second interference pattern comprises at least two diffraction orders, wherein the object is positioned within an overlap of said at least two diffraction orders.

11. A method for measuring surface characteristics of at least a portion of an object comprising:
providing at least one light source;
directing light from the at least one light source to generate a first interference pattern on the at least a portion of the object;
capturing at least one first image of the first interference pattern;
shifting the phase of the at least one light source to generate a second interference pattern;
capturing at least one second image of the second interference pattern;
filtering distortion from the first interference pattern and/or the second interference pattern;
extracting a wrapped phase of the at least a portion of the object based on the at least one first image and the at least one second image;
unwrapping the wrapped phase of the at least a portion of the object to generate an unwrapped phase;
identifying a computed depth map distance to the at least a portion of the object based on the unwrapped phase; and
fitting an ideal part to the computed depth map of the at least a portion of the object to measure the surface characteristics,
wherein the object is at least partially submerged in an optically distorting liquid medium of variable and changing indexes of refraction, and
wherein said filtering distortion comprises factoring an image tensor into a low rank subspace plus a sparse tensor and utilizing a loss function, wherein the loss function includes a quadratic term for the low rank subspace and at least one term for the sparse component.

12. The method of claim 11 , wherein the low rank subspace includes information relating to how a given phase correlates to a projected interference pattern, wherein the low rank substance includes information relating to changes over time due to relative movement of the object.

13. A method for measuring surface characteristics of at least a portion of an object comprising:
providing at least one light source;
directing light from the at least one light source to generate a first interference pattern on the at least a portion of the object;
capturing at least one first image

Assignees

• Electric Power Res Institute Inc

Inventors

• Stoutamire David
• Hussey Dennis

Classifications

• G06T2207/30108

  Industrial image inspection · CPC title

• G06T7/521

  from laser ranging, e.g. using interferometry; from the projection of structured light · CPC title

• G01B11/026

  by measuring distance between sensor and object (G01B11/0608 takes precedence) · CPC title

• G01B11/2441

  using interferometry · CPC title

• Y02E30/30

  Nuclear fission reactors · CPC title