RETROREFLECTIVE SURFACE

• US 3,712,706 A
• Filed: 01/04/1971
• Issued: 01/23/1973
• Est. Priority Date: 01/04/1971
• Status: Expired due to Term

• Current Assignee: Robert Franz Stamm
• Original Assignee: Robert Franz Stamm
• Inventors: Stamm, Robert Franz
• Primary Examiner(s): Schonberg, David
• Assistant Examiner(s): Tokar, Michael J.
• Application Number:
  US05/103,543
• Time in Patent Office: 750 Days
• Field of Search: 350/97-109,162R,286,287,129 94/1.5
• US Class Current: 359/531
• CPC Class Codes: G02B 5/124 plural reflecting elements forming part of a unitary plate or sheet

Abstract

A retroreflector of unusually high retroreflective efficiency comprises an array of cube corner reflectors arranged as shown in FIG. 1. The cube corners are made so extremely accurately and of such small size teat diffraction is the predominant factor governing the divergence from perfect retroreflection of the reflected light. The retroreflectors have various uses and are particularly efficient reflectors for highway signs and markers.

Claims

1. A retroreflector constructed so that diffraction is a dominant factor governing the angular divergence of retroreflected light from perfect retroreflection, said retroreflector consisting essentially of a hexagonal close packed array of contiguous cube corners having windows which are equilateral triangles defined at the intersecting boundaries of respective contiguous cube corners in said array by three sets of continuous parallel lines all oriented in a plane with included angles of 60* between respective lines of each such set at a common point of intersection, said cube corners each having three adjacent faces intersecting at dihedral angles of 90* + OR 2.8 minutes of arc, the respective adjacent lines in each such three sets of parallel boundary lines being all equally spaced apart with normal spacing in the range from 15.5 to 830 microns between adjacent lines of each set, said normal spacing of parallel lines being a value within the defined range selected to produce a desired angular divergence of the retroreflected light due to diffraction, and the faces of said cube corners all being essentially specular mirror surfaces having reflective coefficients of at least 0.6.

2. A retroreflector defined by claim 1 wherein the defined array of cube corners is defined as cavities in the surface of a thin sheet of plastic resin material.

3. A retroreflector defined by claim 1 wherein the defined array of cube corners is defined as cavities in a metal surface.

4. A retroreflector defined by claim 1 wherein the defined array of cube corners are cavities filled with optically transparent solid material.

5. A retroreflector defined by claim 1 wherein the defined array of cube corners consists of transparent cube corner prisms formed in and projecting from the back of a sheet of transparent sheet material.

6. A retroreflector defined by claim 5 having the faces of the defined prisms in contact with air and the prisms being retroreflective by total internal reflection.

7. A retroreflector defined by claim 5 having the outer prism surfaces coated with evaporated metal mirror coating and a protective covering.

8. A retroreflector defined by claim 1 wherein the defined normal spacing between parallel boundary lines is about 254 microns.

9. A retroreflector defined by claim 1 wherein the defined specular reflective coefficient of each mirror surface is about 0.9.

10. A retroreflector defined by claim 1 wherein each cube corner face in the array is cylindrically concave outward between base and apex with radius of curvature less than 400 feet.

11. A retRoreflector defined by claim 10 wherein the defined radius of curvature is about 200 feet.

12. A retroreflector defined by claim 3 wherein the front surface of plastic material through which incident and retroreflected light are transmitted and refracted, forms a spherical convex lens surface having radius of curvature less than 400 feet.

13. A retroreflector defined by claim 12 wherein the defined radius of curvature is about 200 feet.

14. A retroreflector constructed so that diffraction is a dominant factor governing the angular divergence of retroreflected light from perfect retroreflection, said retroreflector consisting essentially of a hexagonal close packed array of contiguous cube corners having windows which are equilateral triangles defined at the intersecting boundaries of respective contiguous cube corners in said array by three sets of continuous parallel lines all oriented in a plane with included angles of 60* between respective lines of each such set at a common point of intersection, said cube corners each having three adjacent faces intersecting at dihedral angles two of which are 90* + or - 2.8 minutes of arc and the other is 90* + or - 2*, the respective adjacent lines in each such three sets of parallel boundary lines being all equally spaced apart with normal spacing in the range from 3.5 to 250 microns between adjacent lines of each set, said normal spacing of parallel lines being a value within the defined range selected to produce a desired angular divergence of the retroreflected light due to diffraction, and the faces of said cube corners all being essentially specular mirror surfaces having reflective coefficients of at least 0.6.

15. A retroreflector constructed so that diffraction is a dominant factor governing the angular divergence of retroreflected light from perfect retroreflection, said retroreflector consisting essentially of a hexagonal close packed array of contiguous cube corners having windows which are equilateral triangles defined at the intersecting boundaries of respective contiguous cube corners in said array by three sets of continuous parallel lines all oriented in a plane with included angles of 60* between respective lines of each such set at a common point of intersection, said cube corners each having three adjacent faces intersecting at dihedral angles one of which is 90* + or - 2.8 minutes of arc and the other two are 90* + or -2.0*, the respective adjacent lines in each such three sets of parallel boundary lines being all equally spaced apart with normal spacing in the range from 3.5 to 250 microns between adjacent lines of each set, said normal spacing of parallel lines being a value within the defined range selected to produce a desired angular divergence of the retroreflected light due to diffraction, and the faces of said cube corners all being essentially specular mirror surfaces having reflective coefficients of at least 0.6.

16. A retroreflector constructed so that diffraction is a dominant factor governing the angular divergence of retroreflected light from perfect retroreflection, said retroreflector consisting essentially of a hexagonal close packed array of contiguous cube corners having windows which are equilateral triangles defined at the intersecting boundaries of respective contiguous cube corners in said array by three sets of continuous parallel lines all oriented in a plane with included angles of 60* between respective lines of each such set at a common point of intersection, said cube corners each having three adjacent faces intersecting at dihedral angles of 90* + or -2*, the respective adjacent lines in each such three sets of parallel boundary lines being all equally spaced apart with normal spacing in the range from 3.5 to 250 microns between adjacent lines of each set, said normal spacing of parallel lines being a value within the defiNed range selected to produce a desired angular divergence of the retroreflected light due to diffraction, and the faces of said cube corners all being essentially specular mirror surfaces having reflective coefficients of at least 0.6.