Methods and apparatus for a self-aligned digital projection and reflected glare reduction imaging system

Patent metadata

Field	Value
Publication number	US-12072286-B2
Application number	US-202117490612-A
Country	US
Kind code	B2
Filing date	Sep 30, 2021
Priority date	Mar 19, 2021
Publication date	Aug 27, 2024
Grant date	Aug 27, 2024

Abstract

A digital projection and reflected glare reduction system according to various aspects of the present technology may include a digital display device capable of generating a one or two dimensional source grid pattern back-illuminated by a light source to project an image of a source grid onto a retroreflective background. The projected source grid image may then be re-imaged onto the original grid element at a slight offset eliminating the need to generate a separate cutoff grid thereby reducing the amount of time required to setup and adjust the system. The digital display device is also capable of switching between a schlieren visualization capability to some other visualization capability (such as particle tracking velocimetry (PTV), particle imaging velocimetry (NV), temperature sensitive paint measurements (TSP), pressure sensitive paint measurements (PSP), photogrammetry, etc.) allowing for the simultaneous use of two different imaging techniques.

First claim

What is claimed is:

1. A digital projection focusing optical system for measuring a test object in a test section of an instrument, comprising:
a beam splitter configured to reflect an incident linear vertically polarized (LVP) light from a light source along an optical axis of the optical system;
an LCD element positioned to receive the LVP light from the beam splitter, wherein the LCD element comprises a selectable pixel element configured to:
generate a source grid comprising regions of the selectable pixel element switchable between a transparent state and an opaque state; and
rotate the LVP light by ninety degrees to be liner horizontally polarized (LHP) light when regions of the generated source grid are in the transparent state;

a polarizing prism configured to receive the LHP light from the LCD element and split the LHP light into two light beams, wherein:
a first light beam comprising LHP light is refracted by a small angle relative to the optical axis and exits the polarizing prism at that small angle; and
a second light beam comprising LVP light continues along and exits the polarizing prism aligned with the optical axis;

a quarter-wave plate positioned between the polarizing prism and a retroreflective background, wherein the quarter-wave plate is configured to:
modify the LVP light exiting the polarizing prism to right circularly polarized (RCP) light; and
modify the LHP light exiting the polarizing prism to left circularly polarized (LCP) light; and

an imaging lens positioned between the LCD element and the test section, wherein the imaging lens is configured to project the generated source grid onto the retroreflective background, wherein:
the retroreflective background is configured to:
reflect the incoming RCP light back towards the quarter wave plate and reverse the RCP light to LCP light;
reflect the incoming LCP light back towards the quarter wave plate and reverse the LCP light to RCP light; and
reflect an image of the projected source grid; and

the imaging lens projects the reflected image of the source grid back onto the LCD element.

2. A digital projection focusing optical system according to claim 1 , further comprising a linear polarizer positioned to receive the reflected RCP light and LCP light from the retroreflective background.

3. A digital projection focusing optical system according to claim 1 , further comprising a linear polarizer positioned between the light source and the beam splitter to provide the LVP light to the beam splitter.

4. A digital projection focusing optical system according to claim 3 , further comprising a condenser lens positioned between the light source and the linear polarizer.

5. A digital projection focusing optical system according to claim 1 , wherein the LCD element comprises:
a first polarizer positioned on a first side of the LCD element adjacent the selectable pixel element; and
a second polarizer positioned on a second side of the LCD element, wherein the selectable pixel element is positioned between the first and second polarizers.

6. A digital projection focusing optical system according to claim 5 , wherein:
a transmission axis of the first polarizer comprises a transmission axis aligned with the beam splitter; and
a transmission axis of the second polarizer is orthogonal to the transmission axis of the first polarizer.

7. A digital projection focusing optical system according to claim 1 , wherein the beam splitter comprises a polarizing beam splitter configured to reflect LVP light along the optical axis of the instrument.

8. A digital projection focusing optical system according to claim 7 , further comprising a half-wave plate positioned between the LCD element and the polarizing prism.

9. A method of measuring a test object in a test section of an instrument with a digital projection focusing optical system, comprising:
directing an incident light source towards a beam splitter configured to reflect linear vertically polarized (LVP) light along an optical axis of the optical system towards an LCD element comprising a selectable pixel element;
generating a source grid comprising regions of the selectable pixel element switchable between a transparent state and an opaque state;
rotating the LVP light by ninety degrees to be liner horizontally polarized (LHP) light when regions of the generated source grid are in the transparent state;
receiving the light from the LCD element with a polarizing prism configured to split the light into:
a first light beam comprising LHP light is refracted by a small angle relative to the optical axis and exits the polarizing prism at that angle; and
a second light beam comprising LVP light continues along and exits the polarizing prism aligned with the optical axis;

passing the first and second light beams through a quarter-wave plate, wherein the quarter-wave plate is configured to:
modify the first light beam exiting the polarizing prism at the small angle to left circularly polarized (LCP) light; and
modify the second light beam exiting the polarizing prism along the optical axis to right circularly polarized (RCP) light;

projecting the source grid generated by the LCD element onto a retroreflective background with an imaging lens;
passing the RCP light and the LCP light beams through the test section and onto a retroreflective background, wherein the retroreflective background is configured to:
reflect the incoming first light beam back through the test section at the small angle towards the quarter-wave plate as RCP light;
reflect the incoming second light beam back through the test section along the optical axis towards the quarter-wave plate as LCP light; and
reflected the projected source grid;

passing the reflected first and second light beams through a quarter-wave plate a second time, wherein:
the reflected first light beam passes through the quarter-wave plate at the small angle and is converted into LVP light;
the reflected second light beam passes through the quarter-wave plate along the optical axis and is converted into LHP light;

passing the reflected first and second light beams through the polarizing prism a second time, wherein:
the first light beam continues through the polarizing prism at the small angle; and
the second light beam is refracted by the small angle relative to the optical axis and exits the polarizing prism at the small angle; and

projecting the reflected source grid onto the LCD element with the imaging lens;
passing the first and second light beams to the LCD element, wherein at least one of the first and second light beams is prevented from passing through the LCD element; and
the remaining light beam is directed through the beam splitter at the small angle to a sensor element.

10. A method of measuring a test object according to claim 9 , further comprising positioning a linear polarizer between the beam splitter and the sensor element.

11. A method of measuring a test object according to claim 9 , further comprising positioning a linear polarizer between the light source and the beam splitter.

12. A method of measuring a test object according to claim 11 , further comprising positioning a condenser lens between the light source and the linear polarizer.

13. A method of measuring a test object according to claim 9 , wherein the LCD element comprises:
a first polarizer positioned on a first side of the LCD element adjacent the selectable pixel element; and
a second polarizer positioned on a second side of the LCD element, wherein:
the selectable pixel element is positioned between the first and second polarizers; and
the second polarizer is orie

Assignees

• Nasa

Inventors

• Bathel Brett F
• Weisberger Joshua M

Classifications

• G01N21/958

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

• G02B27/54

  Schlieren-optical systems · CPC title

• G02B27/283

  used for beam splitting or combining · CPC title

• G01N21/21

  Polarisation-affecting properties (G01N21/19 takes precedence) · CPC title

• G01N21/455 Primary

  Schlieren methods, e.g. for gradient index determination; Shadowgraph · CPC title