Optical mark reader
View Patent ↗Each data point within a two-dimensional code can be represented by a distribution of spots. Each spot can be made small enough to be invisible to the human eye so that the two-dimensional code can be invisible on or within transparent or nontransparent materials. The spots can be spaced at a large distance to increase the signal-to-noise ratio for an optical code reader. A code reader can be adapted to read the spots and determine the data points.
1. A method for reading a two-dimensional identification code within a substrate having first and second opposing surfaces, comprising:
directing light toward a first surface of the substrate, wherein the light has a wavelength, and wherein the substrate is transparent to the wavelength, wherein the two-dimensional code is represented by a distribution of spots within the substrate, wherein the distribution of spots comprises multiple groups of spots, including first and second groups of spots, wherein each of the first and second groups of spots is representative of a geometric shape, such that the distribution of spots forms an array of multiple rows and columns of geometric areas, wherein some of the geometric areas include one group of spots and some of the geometric areas are devoid of spots, wherein a first portion of the light is blocked by the spots, and wherein a second portion of the light passes beyond the spots and propagates through the second surface of the substrate;
magnifying the second portion of the light that propagates through the second surface of the substrate;
imaging with an imager the second portion the light that propagates through the second surface of the substrate and is magnified;
analyzing an image of the second portion of the light and shadows caused by blockage of the first portion of the light to determine the distribution of the spots; and
determining the two-dimensional code based on the distribution of the spots imaged by the imager.
2. The method of claim 1 , wherein the step of magnifying employs an optical system capable of achieving a modulation transfer function of greater than 80 line pairs/millimeter.
3. The method of claim 1 , wherein the representative geometric shape is a rectangular geometric shape, and wherein the first and second groups of spots are positioned to represent corners of the rectangular geometric shape.
4. The method of claim 1 , wherein the array has an array dimension that is smaller than 500 microns.
5. The method of claim 1 , wherein the first and second groups of spots are invisible to the human eye at a distance of greater than or equal to 25 mm from the human eye.
6. The method of claim 1 , wherein the spots of the first and second groups each have a dimension for a major spatial axis that is smaller than 35 microns.
7. The method of claim 1 , wherein the spots each have a dimension for a major spatial axis, and wherein the spots are separated by a distance that is greater than or equal to four times the dimension of the major spatial axis.
8. The method of claim 1 , wherein the spots are dark and the substrate is light.
9. The method of claim 1 , wherein the spots are dark, and wherein the substrate is substantially transparent to visible light.
10. The method of claim 1 , wherein the substrate comprises at least one of a crystalline material, a noncrystalline material, sapphire, glass, plastic, and aluminum.
11. The method of claim 1 , wherein the group of spots provides a signal to noise ratio of greater than or equal to 10.
12. The method of claim 1 , wherein the array comprises at least 50 geometric areas in a row or a column.
13. The method of claim 1 , wherein the light source is positioned to propagate the light along an illumination path that traverses the first surface, and wherein the illumination path traverses the first surface at a perpendicular angle.
14. The method of claim 1 , wherein the light source is positioned to propagate the light along an illumination path that traverses the first surface, and wherein the light source is positioned along an illumination axis that is generally perpendicular to the first surface of the substrate.
15. The method of claim 14 , wherein the imager is positioned along the illumination axis.
16. The method of claim 1 , wherein the light source is positioned to propagate the light along an illumination path that traverses the first surface, and wherein the light source is positioned along an illumination axis that has a non-perpendicular angle of incidence to the first surface of the substrate.
17. The method of claim 16 , wherein the illumination axis has an angle of incidence of between 10 and 65 degrees.
18. The method of claim 1 , wherein the imager is positioned along an imaging axis that is perpendicular to the first surface.
19. The method of claim 1 , wherein the light is generated by a light source that comprises an LED.
20. The method of claim 1 , wherein an optical system magnifies the second portion of the light that propagates through the second surface of the substrate, and wherein the optical system employs optics that provide greater than five times magnification.
21. The method of claim 1 , wherein an optical system magnifies the second portion of the light that propagates through the second surface of the substrate, and wherein the optical system provides a depth of field within about +/−50 μm.
22. The method of claim 1 , wherein an optical system magnifies the second portion of the light that propagates through the second surface of the substrate, and wherein the optical system provides a field of view that is greater than or equal to about 500 μm.
23. The method of claim 1 , wherein the spots form a 2DID code having a field size with a side dimension smaller than 500 microns.
24. The method of claim 1 , wherein the spots form a GS1 DataMatrix code having a field size with two dimensions smaller than 125 microns.
25. The method of claim 1 , wherein each spot is formed by a laser pulse.
26. The method of claim 1 , wherein one or more of the spots has a positioning accuracy with respect to a desired location that is worse than 5 microns.
27. The method of claim 1 , wherein each spot has a spot area, wherein a cumulative spot area represents spot areas of the spots within one group of spots, wherein the distribution of spots in a group is spread over a group area, wherein the cumulative spot area is smaller than or equal to less than 5% of the group area.
28. The method of claim 1 , wherein the imager is monochromatic.
29. The method of claim 1 , wherein the imager is full color.
30. The method of claim 1 , wherein an optical system magnifies the second portion of the light that propagates through the second surface of the substrate, and wherein the optical system provides a depth of field within about +/−10 μm.
31. The method of claim 1 , wherein the geometric areas represent squares in a QR code.
32. A method for reading a two-dimensional identification code within a substrate having first and second opposing surfaces, comprising:
directing light toward the first surface of the substrate, wherein the light has a wavelength, and wherein the substrate and its first surface are transparent to the wavelength, wherein the two-dimensional code is represented by a distribution of spots within the substrate, wherein the distribution of spots comprises multiple groups of spots, including first and second groups of spots, wherein each of the first and second groups of spots is representative of a geometric shape, such that the distribution of spots forms an array of multiple rows and columns of geometric areas, wherein some of the geometric areas include one group of spots and some of the geometric areas are devoid of spots, wherein a first portion of the light passes beyond the spots and is absorbed at the second surface, wherein the second surface or a coating applied thereon is absorptive to the wavelength, and wherein a second portion of the light passes beyond the spots and propagates through the second surface of the substrate through the first surface;
magnifying the second portion of the light that propagates through the first surface;
imaging with an imager the second portion of the light that propagates through the first surface and is magnified;
analyzing an image of the second portion of the light and a dark background caused by absorption of the first portion of the light to determine the distribution of the spots; and
determining the two-dimensional code based on the distribution of the spots imaged by the imager.
33. A method for reading a two-dimensional identification code within a substrate having first and second opposing surfaces, comprising:
directing light toward the first surface of the substrate, wherein the light has a wavelength, and wherein the substrate and its first surface are transparent to the wavelength, wherein the two-dimensional code is represented by a distribution of spots within the substrate, wherein the distribution of spots comprises multiple groups of spots, including first and second groups of spots, wherein each of the first and second groups of spots is representative of a geometric shape, such that the distribution of spots forms an array of multiple rows and columns of geometric areas, wherein some of the geometric areas include one group of spots and some of the geometric areas are devoid of spots, wherein some of the light passes beyond the spots and becomes reflected light by the second surface, wherein the second surface or a coating applied thereon is reflective to the wavelength, wherein a first portion of the reflected light is blocked by the spots, and wherein a second portion of the reflected light passes beyond the spots and propagates through the first surface of the substrate;
magnifying the second portion of the reflected light that propagates through the first surface;
imaging with an imager the second portion the reflected light that propagates through the second surface of the substrate and is magnified;
analyzing an image of the second portion of the reflected light and shadows caused by blockage of the first portion of the reflected light to determine the distribution of the spots; and
determining the two-dimensional code based on the distribution of the spots imaged by the imager.