Flatness tester for optical components
View Patent ↗Disclosed herein is a method comprising capturing an image of a grating formed on a surface of a brightness enhancing display film; measuring a displacement Δd of a fringe from the image of the grating; and determining a slope of a deviation from flatness of the brightness enhancing display film from the displacement Δd by using the equation (I) Δ d ( y , θ 2 ) = 2 y sin ( θ 1 + θ 3 - 2 θ 2 ) [ tan ( θ 1 + θ 3 - θ 2 - 90 ) tan ( 90 - θ 2 ) + tan ( θ 1 + θ 3 - θ 2 - 90 ) ] ( I ) wherein y represents a distance along the brightness enhancing display film that represents a location of the deviation from flatness; θ 1 is a light box angle; θ 2 is the slope of the deviation from flatness in the brightness enhancing display film; and θ 3 is a camera angle.
1. A method comprising:
capturing an image of a grating formed on a surface of a brightness enhancing display film;
measuring a displacement Δd of a fringe from the image of the grating; and
determining a slope of a deviation from flatness of the brightness enhancing display film from the displacement Δd by using the equation (I)
Δ
d
(
y
,
θ
2
)
=
2
y
sin
(
θ
1
+
θ
3
-
2
θ
2
)
[
tan
(
θ
1
+
θ
3
-
θ
2
-
90
)
tan
(
90
-
θ
2
)
+
tan
(
θ
1
+
θ
3
-
θ
2
-
90
)
]
(
I
)
wherein y represents a distance along the brightness enhancing display film that represents a location of the deviation from flatness; θ 1 is a light box angle; θ 2 is the slope of the deviation from flatness in the brightness enhancing display film; and θ 3 is a camera angle.
2. The method of claim 1 , further comprising determining a rate of deviation from flatness by taking a derivative of the slope of the deviation from flatness.
3. The method of claim 2 , further comprising rejecting a brightness enhancing display film when the rate of deviation from flatness exceeds 0.0004 degrees per minute.
4. The method of claim 1 , wherein the sum of the light box angle θ 1 and the camera angle θ 3 is less than or equal to about 90 degrees.
5. The method of claim 1 , wherein the sum of the light box angle θ 1 and the camera angle θ 3 is greater than 90 degrees.
6. The method of claim 1 , wherein the sum of the light box angle θ 1 and the camera angle θ 3 is equal to about 116 degrees.
7. The method of claim 6 , wherein the wherein the slope of the deviation from flatness of the brightness enhancing display film can be determined by using the equation (III)
Δd=0.0153yθ 2 (III)
wherein y represents a distance along the brightness enhancing display film that represents a location of the deviation from flatness.
8. The method of claim 7 , further comprising graphically representing the relationship between Δd and θ 2 in order to obtain the slope of the deviation from flatness.
9. The method of claim 1 , further comprising graphically representing the relationship between Δd and θ 2 in order to obtain the slope of the deviation from flatness.
10. The method of claim 1 , wherein the surface of the brightness enhancing display film is a back surface.
11. The method of claim 10 , wherein a beam of light transmitted through the grating is incident upon the brightness enhancing display film in a direction perpendicular to a prism line.
12. The method of claim 1 , wherein the surface of the brightness enhancing display film is a prism surface.
13. The method of claim 12 , wherein a beam of light transmitted through the grating is incident upon the brightness enhancing display film in a direction parallel to a prism line.
14. An apparatus that employs the method of claim 1 .
15. An apparatus comprising:
a light box;
a grating disposed thereon;
a platform for holding a brightness enhancing display film; and
a camera for recording an image of the grating on the brightness enhancing display film; wherein the image can be used to measure a displacement Δd of a fringe from the image of the grating and determine a slope of a deviation from flatness of the brightness enhancing display film from the displacement Δd by using the equation (I)
Δ
d
(
y
,
θ
2
)
=
2
y
sin
(
θ
1
+
θ
3
-
2
θ
2
)
[
tan
(
θ
1
+
θ
3
-
θ
2
-
90
)
tan
(
90
-
θ
2
)
+
tan
(
θ
1
+
θ
3
-
θ
2
-
90
)
]
(
I
)
wherein y represents a distance along the brightness enhancing display film that represents a location of the deviation from flatness; θ 1 is a light box angle; θ 2 is the slope of the deviation from flatness in the brightness enhancing display film; and θ 3 is a camera angle.
16. The apparatus of claim 15 , further comprising a computer, wherein the computer executes an algorithm that is operative to facilitate the apparatus in:
capturing an image of a grating formed on a surface of a brightness enhancing display film;
measuring the displacement Δd of the fringe from the image of the grating; and
determining the slope of the deviation from flatness of the brightness enhancing display film.