Machine-vision illumination system and method for delineating a lighted volume from an unlighted volume

• US 5,745,176 A
• Filed: 10/12/1995
• Issued: 04/28/1998
• Est. Priority Date: 10/12/1995
• Status: Expired due to Term

• Current Assignee: Datalogic Automation Incorporated (Datalogic S.p.A.)
• Original Assignee: PPT Vision, Inc. (Datalogic S.p.A.)
• Inventors: Lebens, Gary A.
• Primary Examiner(s): Tran, Thai
• Assistant Examiner(s): Vu, Ngoc-Yen, VU, NGOC YEN T
• Application Number:
  US08/532,213
• Time in Patent Office: 929 Days
• Field of Search: 359/738, 359/739, 362/234, 362/235, 362/236, 362/244, 362/248, 348/86, 348/87, 348/370, 348/371, 348/125, 348/126, 348/127, 348/128, 348/131, 348/132
• US Class Current: 348/370
• CPC Class Codes: G01N 21/8806 Specially adapted optical and illumination features

Abstract

The present invention takes advantage of the efficiency of high-brightness red, infra-red, or other color LEDs arranged in a single row, the properties inherent to a focusing element such as a cylindrical lens, as well as the advantages of having a straight-edged diaphragm and a light-absorbing enclosure to produce an illumination source for machine-vision systems. The illumination source exhibits multi-directional properties on one side of an imaginary plane defined by the positions of the row of LEDs, the straight-edged diaphragm, and the focusing element, and minimize light cast on the other side of the plane. The present invention provides a compact light line generator which has no shadowing or secondary lines. The present invention also provides a method for measuring the height of a raised surface. The present invention provides a method and apparatus which provide an illumination source for illuminating an object in a machine-vision system, and includes a light source emitting light from a plurality of points, the points being on a straight line, a focusing element, the focusing element focusing light from the light source in one dimension to a focal line, wherein the focusing element is separated from the straight line by a distance sufficient to focus rays from the plurality of points into the focal line, and wherein there is a light path from the straight line to the focusing element and then to the focal line, and a first diaphragm located in the light path and defining a sharp edge in the rays. This embodiment provides a light which has a sharply defined virtual surface which separates lighted areas from areas not lit, and within the lighted areas, provides light from multiple directions to reduce shadowing.

Claims

1. An illumination source for illuminating an object in a machine-vision system the machine-vision system including an imaging device that has an optical axis, comprising:

a light source that emits non-collimated light from a plurality of locations, the locations being on a substantially straight line;

a focusing element, the focusing element focusing light from the light source in one dimension to a focal line, wherein the focusing element is separated from the straight line by a distance sufficient to focus rays from the plurality of locations into the focal line, and wherein there is a light path from the straight line to the focusing element and then to the focal line; and

a first diaphragm located in the light path between the light source and the focal line and defining a sharp edge in the rays in order to produce a surface substantially delineating a illuminated volume having light from the light source from an unilluminated volume that has substantially no light from the light source and substantially less light overall, and wherein the optical axis of the imaging device passes through the surface such that a portion of the object viewable by the imaging device lies within the illuminated volume and another portion of the object otherwise viewable by the imaging device lies in the unilluminated volume.

2. The illumination source as recited in claim 1, wherein the first diaphragm has at least one straight-line segment lying substantially within a plane which also contains substantially the surface and the straight line of the light source.

3. The illumination source as recited in claim 2, further comprising an enclosure having an interior surface which is anti-reflective at a wavelength of the light source, the straight line of the light source being located inside the enclosure.

4. The illumination source as recited in claim 3 wherein the focusing element is a plano-convex cylindrical lens having a flat surface and a cylindrical surface.

5. The illumination source as recited in claim 4, wherein the first diaphragm has a straight edge located near the cylindrical surface of the cylindrical lens, and further comprising a second straight-edged diaphragm having a straight edge located near the flat surface of the cylindrical lens to reduce reflections from the light source.

6. The illumination source as recited in claim 1 wherein the light source comprises at least one light-emitting diode (LED) which emits light.

7. The illumination source as recited in claim 6 wherein the light emitted from the LEDs is blue in color.

8. The illumination source as recited in claim 7 wherein the light emitted from the LEDs is at an angle of about 22.5°

from a center line of each individual LED.

9. A method for illuminating an object in a machine-vision system the machine-vision system including an imaging device that has an optical axis, comprising the steps of:

(a) emitting non-collimated light from a plurality of locations, the locations being on a substantially straight line;

(b) focusing the emitted light from the plurality of locations into a focal line, and wherein there is a light path from the straight line to a focusing element and then to the focal line; and

(c) defining a sharp edge in the rays in order to produce a surface substantially delineating a illuminated volume having light from the light source from an unilluminated volume that has substantially no light from the light source and substantially less light overall, and wherein the optical axis of the imaging device passes through the surface such that a portion of the object viewable by the imaging device lies within the illuminated volume and another portion of the object otherwise viewable by the imaging device lies in the unilluminated volume.

10. The method for illuminating an object as recited in claim 9, wherein the step 2 of defining includes providing at least one straight-line diaphragm segment lying substantially within a plane which also contains substantially the surface and the straight line of the emitted light.

11. The method for illuminating an object as recited in claim 10, further comprising the step of enclosing the straight line and the focusing element with an enclosure having an interior surface which is anti-reflective at a wavelength of the emitted light.

12. The method for illuminating an object as recited in claim 9, wherein the step of emitting comprises emitting light from at least one light-emitting diode (LED).

13. The method for illuminating an object as recited in claim 12, wherein the object is an electrical connector, and further including the step of inspecting an aspect of the connector that affects functionality of the connector.

14. The method for illuminating an object as recited in claim 12, wherein the light emitted from the LEDs is at an angle of about 22.5°

from a center line of each individual LED.

15. The method for illuminating an object as recited in claim 9, wherein the focusing element is a plano-convex cylindrical lens having a flat surface and a cylindrical surface.

16. The method for illuminating an object as recited in claim 15, wherein, step of defining includes providing at least a first diaphragm has a straight edge, and the step of placing includes locating the straight edge near the cylindrical surface of the cylindrical lens, and further comprising the step of placing a second straight-edged diaphragm having a straight edge located near the flat surface of the cylindrical lens to reduce reflections from the light source.

17. A machine-vision illumination system, comprising:

an imaging device that has an optical axis;

an image processor coupled to the imaging device; and

an illumination source coupled to the image processor, the illumination source comprising;

a light source that emits non-collimated light from a plurality of locations, the locations being on a substantially straight line,

a focusing element, the focusing element focusing light from the light source in one dimension to a focal line, wherein the focusing element is separated from the straight line by a distance sufficient to focus rays from the plurality of locations into the focal line, and wherein there is a light path from the straight line to the focusing element and then to the focal line, and

a first diaphragm located in the light path and defining a sharp edge in the rays in order to produce a surface substantially delineating a illuminated volume having light from the light source from an unilluminated volume that has substantially no light from the light source and substantially less light overall, and wherein the optical axis of the imaging device passes through the surface such that a portion of the object viewable by the imaging device lies within the illuminated volume and another portion of the object otherwise viewable by the imaging device lies in the unilluminated volume.

18. The machine-vision illumination system as recited in claim 17, wherein the first diaphragm has at least one straight-line segment lying substantially within a plane which also contains substantially the surface and the straight line of the light source.

19. The machine-vision illumination system as recited in claim 18, further comprising an enclosure having an interior surface which is anti-reflective at a wavelength of the light source, the straight line of the light source being located inside the enclosure.

20. The machine-vision illumination system as recited in claim 19 wherein the focusing element is a piano-convex cylindrical lens having a flat surface and a cylindrical surface.

21. The machine-vision illumination system as recited in claim 20, wherein the first diaphragm has a straight edge located near the cylindrical surface of the cylindrical lens, and further comprising a second straight-edged diaphragm having a straight edge located near the flat surface of the cylindrical lens to reduce reflections from the light source.

22. The machine-vision illumination system as recited in claim 17 wherein the light source comprises at least one light-emitting diode (LED) which emits light.

23. The machine-vision illumination system as recited in claim 20 wherein the light emitted from the LEDs is blue in color.

24. The machine-vision illumination system as recited in claim 23 wherein the light emitted from the LEDs is at an angle of about 22.5°

from a center line of each individual LED.