Position sensing systems for use in touch screens and prismatic film used therein
View Patent ↗A dual light-source position detecting system for use in touch screens is provided that utilizes parallax to determine the position of an interposing object, and a prismatic film that is brightly retroreflective over a broad entrance angle to enhance to accuracy of the parallax determination of position. The position detecting system includes at least one camera positioned to receive light radiation traversing a detection area and that generates a signal representative of an image; two spaced-apart sources of light radiation, which may be LEDs, or IR emitters positioned adjacent to the camera for outputting light radiation that overlaps over at least a portion of a detection area, and a prismatic film positioned along a periphery of at least a portion of the detection area that retroreflects the light radiation from the two sources to the camera.
1. A position detection system comprising:
a camera positioned to receive electromagnetic radiation traversing a detection area that generates a signal representative of an image;
a dual source of electromagnetic radiation positioned adjacent to said camera for outputting electromagnetic radiation that overlaps over at least a portion of a detection area, and
a prismatic film positioned along a periphery of at least a portion of the detection area that retroreflects said electromagnetic radiation from said source to said camera, wherein the prismatic film includes a plurality of individual triangular cube corner retroreflective elements having dihedral angle errors e 1 , e 2 , and e 3 such that e 1 ≈e 2 ≠0 and e 3 ≈0, and wherein e 1 and e 2 are either both positive or both negative in each individual triangular cube corner element.
2. The system of claim 1 , wherein the source of electromagnetic radiation is a pair of IR emitters.
3. The system of claim 1 , wherein |e 1 | and |e 2 | are between 0.03° and 0.20°.
4. The system of claim 1 , wherein said plurality of triangular cube corner elements are canted between 8° and 24°.
5. The system of claim 1 , wherein said triangular cube corner retroreflective elements have a cube depth of between 0.002 and 0.0055 inches.
6. A prismatic film, comprising:
an unpinned prismatic film having a retroreflective substrate including a plurality of individual triangular cube corner retroreflective elements, and
wherein the retroreflective cube corner elements have dihedral angle errors e 1 , e 2 , and e 3 such that e 1 ≈e 2 ≈0 and e 3 ≈0,
wherein each retroreflective cube corner element is defined by a plurality of grooves each having a fixed depth, and
wherein e 1 and e 2 are either both positive or both negative in each individual triangular cube corner element.
7. The prismatic film of claim 6 , further comprising a metallized layer disposed over at least a portion of the cube corner retroreflective elements.
8. The prismatic film of claim 7 , wherein the film is transparent for infra-red light, but is non-transparent for visible light.
9. The prismatic film of claim 7 , wherein the metallized layer is formed from one of aluminum and gold.
10. The prismatic film of claim 6 , wherein said plurality of triangular cube corner elements are canted between 12° and 20°.
11. The prismatic film of claim 6 , wherein said plurality of triangular cube corner elements is canted edge-more-parallel.
12. The prismatic film of claim 6 , wherein about half of the plurality of triangular cube corner retroreflective elements have dihedral angle errors e 1 and e 2 between 0.03° and 0.20° and the remaining half of the plurality of triangular cube corner retroreflective elements have dihedral angle errors e 1 and e 2 between −0.03° and −0.20°.
13. The prismatic film of claim 6 , wherein said triangular cube corner retroreflective elements have a cube depth of between 0.002 and 0.0055 inches.
14. The prismatic film of claim 6 , wherein the first substrate has been dyed with an infra-red dye and appears black in visible light.
15. The prismatic film of claim 6 wherein |e 1 −e 2 |/2>0.03°.
16. The prismatic film of claim 6 wherein |e 1 −e 2 |/2>0.05°.
17. The prismatic film of claim 6 wherein e 3 <0.05°.
18. The prismatic film of claim 6 wherein e3<0.025°.
19. The prismatic film of claim 6 wherein e1−e2<0.06°.
20. The prismatic film of claim 6 wherein e1−e2<0.03°.
21. A prismatic film, comprising;
an unpinned prismatic film having a retroreflective substrate including a plurality of individual triangular cube corner retroreflective elements;
a light source including a pair of point source infrared light emitting diodes;
wherein the light source when reflected produces a pattern of light having a horizontal spread greater than a vertical spread at entrance angles of 0° and 60°;
wherein the triangular cube corner retroreflective elements have dihedral angle errors e 1 , e 2 , and e 3 such that e 1 ≈e 2 ≠0 and e 3 ≈0; and
wherein e 1 and e 2 are either both positive or both negative in each individual triangular cube corner element.
22. A prismatic film as recited in claim 21 , wherein the horizontal spread is at least 1.5 times greater than the vertical spread at entrance angles of 0° and 60°.
23. A prismatic film as recited in claim 22 , wherein total light return at 60° is at least 10% of light return at 0°.
24. A prismatic film as recited in claim 21 , wherein the total light return at 60° is at least 30% of light return at 0°.
25. A prismatic film as recited in claim 21 , wherein the triangular cube corners elements are canted between −10° and −6°.
26. A position detection system comprising:
a camera positioned to receive electromagnetic radiation traversing a detection area that generates a signal representative of an image;
a dual source of electromagnetic radiation positioned adjacent to said camera for outputting electromagnetic radiation that overlaps over at least a portion of a detection area, and
a prismatic film positioned along a periphery of at least a portion of the detection area that retroreflects said electromagnetic radiation from said source to said camera, wherein the prismatic film includes a plurality of individual triangular cube corner retroreflective elements and the radiation source when reflected produces a pattern of light having a horizontal spread greater than a vertical spread at entrance angles of 0° and 60°;
wherein the triangular cube corner retroreflective elements have dihedral angle errors e 1 , e 2 , and e 3 such that e 1 ≈e 2 ≠0 and e 3 ≈0; and
wherein e 1 and e 2 are either both positive or both negative in each individual triangular cube corner element.
27. A prismatic film, comprising:
an unpinned prismatic film having a retroreflective substrate including a plurality of triangular cube corner retroreflective elements,
wherein the retroreflective cube corner elements have dihedral angle errors e 1 , e 2 , and e 3 such that e 1 ≈e 2 ≠0 and e 3 ≈0, wherein the plurality of triangular cube corner elements are canted between −15° and −6°,
wherein each retroreflective cube corner element is defined by a plurality of grooves each having a fixed depth, and
wherein e 1 and e 2 are either both positive or both negative in each individual triangular cube corner element.
28. A prismatic film as recited in claim 27 , wherein the plurality of triangular cube corner elements are canted between −10° and −6°.