Methods and apparatus for optical product inspection

• US 4,906,099 A
• Filed: 10/30/1987
• Issued: 03/06/1990
• Est. Priority Date: 10/30/1987
• Status: Expired due to Term

• Current Assignee: Philip Morris USA Incorporated (Altria Group, Inc.)
• Original Assignee: Philip Morris USA Incorporated (Altria Group, Inc.)
• Inventors: Casasent, David P.
• Primary Examiner(s): Rosenberger, Richard A.
• Application Number:
  US07/115,428
• Time in Patent Office: 858 Days
• Field of Search: 356/394, 382/8, 382/25, 382/41, 382/46, 382/30, 350/433
• US Class Current: 356/394
• CPC Class Codes: G01N 2021/845 Objects on a conveyor
• CPC Class Codes: G01N 2021/8887 based on image processing techniques
• CPC Class Codes: G01N 21/88 Investigating the presence of flaws or contamination
• CPC Class Codes: G06V 10/88 Image or video recognition using optical means, e.g. reference filters, holographic masks, frequency domain filters or spatial domain filters

Abstract

Products having optically detectable straight line segments are inspected for acceptability by forming one or more one-dimensional images of the product in which properly aligned straight line segments are respectively focused to points in the image. Such parameters as the location and image intensity of these one-dimensional image points are used to determine whether or not the product is acceptable. An optical Hough transform underlies these product inspection techniques.

Claims

1. Apparatus for determining whether or not a product has predetermined optically detectable properties including first and second optically detectable straight line segments respectively having first and second predetermined intersecting orientations in a predetermined object plane comprising:

means for forming first and second one-dimensional images of said object plane for said product such that all straight line segments having said first predetermined orientation in said object plane are respectively integrated to points in said first one-dimensional image, and such that all straight line segments having said second predetermined orientation in said object plane are respectively integrated to points in said second one-dimensional image;

means for monitoring said first and second one-dimensional images to determine whether or not said one-dimensional images respectively include points having the image intensities that would result if said object plane for said product included said first and second straight line segments respectively having said first and second predetermined orientations; and

means for producing an output indicative of whether or not said product has said predetermined optically detectable properties based on whether or not said first and second one-dimensional images respectively include points having said image intensities;

wherein said means for forming said first and second one-dimensional images comprises;

a single computer generated hologram for forming said first and second one-dimensional images at respective, spaced, first and second lines.

2. The apparatus defined in claim 1 wherein said means for monitoring said first and second one-dimensional images comprises:

first and second detector means for respectively detecting light at said first and second lines.

3. Apparatus for determining whether or not a product has predetermined optically detectable properties including first and second optically detectable straight line segments respectively having first and second predetermined intersecting orientations in a predetermined object plane comprising:

means for forming first and second one-dimensional images of said object plane for said product such that all straight line segments having said first predetermined orientation in said object plane are respectively integrated to points in said first one-dimensional image, and such that all straight line segments having said second predetermined orientation in said object plane are respectively integrated to points in said second one-dimensional image;

means for monitoring said first and second one-dimensional images to determine whether or not said one-dimensional images respectively include points having the image intensities that would result if said object plane for said product included said first and second straight line segments respectively having said first and second predetermined orientations; and

means for producing an output indicative of whether or not said product has said predetermined optically detectable properties based on whether or not said first and second one-dimensional images respectively include points having said image intensities;

wherein said means for forming said first and second one-dimensional images comprises;

first and second computer generated hologram means respectively forming said first and second one-dimensional images;

deflector means for successively deflecting light from said object plane to said first and second computer generated hologram means; and

means for focusing light from both of said computer generated hologram means to a single line.

4. The apparatus defined in claim 3 wherein said means for monitoring said first and second one-dimensional images comprises:

detector means for detecting light focused to said single line.

5. Apparatus for determining whether or not a product has predetermined optically detectable properties including at least one optically detectable straight line segment parallel to each of a plurality of different predetermined orientations in a predetermined object plane comprising:

a plurality of computer generated holograms;

deflector means for selectively deflecting light from said object plane to any one of said computer generated holograms, said one of said holograms responding by producing a plurality of one-dimensional images of said object plane, each of said one-dimensional images having a longitudinal axis perpendicular to a respective one of a corresponding plurality of said predetermined orientations, the one-dimensional images produced by each hologram being respectively disposed in a plurality of parallel, laterally spaced lines; and

a plurality of detector means, each detecting the light received at a respective one of said parallel, laterally spaced lines.

6. Apparatus for determining whether or not a product has predetermined optically detectable properties including an optically detectable straight line segment parallel to a predetermined orientation in a predetermined object plane comprising:

means for forming a one-dimensional image of said object plane for said product such that all straight line segments parallel to said predetermined orientation in said object plane are respectively integrated to points in said one-dimensional image;

means for monitoring said one-dimensional image to determine whether or not said one-dimensional image includes a point having the image intensity that would result if said object plane for said product included said straight line segment parallel to said predetermined orientation; and

means for producing an output indicative of whether or not said product has said predetermined optically detectable properties based on whether or not said one-dimensional image includes a point having said image intensity;

said means for forming a one-dimensional image including;

spatial light modulator means for receiving light from said object plane for said product and for modulating the reflectivity of an output surface in accordance with said light;

a light source for directing light to said output surface so that it will be reflected from said output surface in accordance with the reflectivity of said output surface; and

means for focusing the light reflected from said output surface to said one-dimensional image.

7. The apparatus defined in claim 6 wherein said light source directs light to said output surface along an axis perpendicular to said surface, and wherein said means for focusing the light reflected from said output surface comprises:

beam splitter means disposed between said light source and said output surface for causing a portion of the light reflected from said output surface to be deflected away from said axis.

8. The apparatus defined in claim 7 wherein said means for focusing the light reflected from said output surface further comprises:

a cylindrical lens having a longitudinal axis parallel to said output surface and perpendicular to said predetermined orientation as said predetermined orientation appears in said portion of the light deflected by said beam splitter means, for focusing said portion of the light deflected by said beam splitter means to said one-dimensional image.

9. The apparatus defined in claim 7 wherein said means for focusing the light reflected from said output surface further comprises:

a Dove prism mounted for rotation about a rotational axis coincident with the axis along which said portion of the light deflected by said beam splitter means travels for producing an image of said portion of said light which is rotated by an amount which is a function of the angle of rotation of said Dove prism about said rotational axis;

means for focusing said rotated image to said one-dimensional image; and

means for rotating said Dove prism to the angle which causes said predetermined orientation as it appears in said rotated image to be perpendicular to the longitudinal axis of said one-dimensional image.

10. The apparatus defined in claim 7 wherein said means for focusing the light reflected from said output surface further comprises:

computer generated hologram means for receiving said portion of the light deflected by said beam splitter means and for focusing said portion of said light to said one-dimensional image.

11. Apparatus for determining whether or not a product has predetermined optically detectable properties including an optically detectable straight line segment parallel to a predetermined orientation in a predetermined object plane comprising:

means for forming a one-dimensional image of said object plane for said product such that all straight line segments parallel to said predetermined orientation in said object plane are respectively integrated to points in said one-dimensional image;

means for monitoring said one-dimensional image to determine whether or not said one-dimensional image includes a point having the image intensity that would result if said object plane for said product included said straight line segment parallel to said predetermined orientation; and

means for producing an output indicative of whether or not said product has said predetermined optically detectable properties based on whether or not said one-dimensional image includes a point having said image intensity;

said means for forming a one-dimensional image comprising;

means for scanning said object plane to produce an output signal sequentially representative of the intensity of the image at each point in said object plane;

a light source;

means for modulating the intensity of the light from said light source in accordance with said scanning means output signal; and

deflector means for selectively deflecting the modulated light from said light source to selected ones of a plurality of points on a one-dimensional image line based on a predetermined mapping function between the points in said object plane and the points on said one-dimensional image line.

12. The apparatus defined in claim 11 wherein said deflector means comprises:

means for producing a mapping signal proportional to said mapping function; and

means responsive to said mapping signal for deflecting the modulated light from said light source by an amount proportional to said mapping signal.

13. The apparatus defined in claim 12 wherein said mapping function is given by the equation p=x Cos θ

+y Sin θ

, where x and y are the object plane point coordinates, θ

is dependent on the angle of said predetermined orientation, and p is the coordinate of the point on said one-dimensional image line.

14. The apparatus defined in claim 13 wherein said means for producing said mapping signal comprises:

means for storing said mapping function; and

means for reading out the stored mapping function in synchronization with said scanning means.

15. The apparatus defined in claim 13 wherein said means for producing said mapping signal comprises:

means for producing first and second output signals respectively proportional to Cosθ and

Sinθ

;

means for multiplying said first output signal by a signal proportional to the x coordinate of the object plane point being scanned by said means for scanning to produce a third output signal;

means for multiplying said second output signal by a signal proportional to the y coordinate of the object plane point being scanned by said means for scanning to produce a fourth output signal; and

means for adding said third and fourth signals together to produce said mapping signal.

16. The apparatus defined in claim 13 wherein said means for producing said mapping signal comprises:

a first light source for producing light having intensity proportional to Cosθ

;

a second light source for producing light having intensity proportional to Sinθ

;

first means responsive to a signal proportional to the x coordinate of the object plane point currently being scanned by said means for scanning for multiplying the light from said first light source by an amount proportional to said x coordinate signal;

second means responsive to a signal proportional to the y coordinate of the object plane point currently being scanned by said means for scanning for multiplying the light from said second light source by an amount proportional to said y coordinate signal;

a photodetector; and

means for focusing light from said first and second means toward said photodetector so that the light applied to said photodetector is proportional to the sum of the fractions of the light from said first and second light sourced reaching said photodetector via said first and second means.

17. The apparatus defined in claim 16 wherein said first and second means respectively comprise:

acousto-optic modulator means.

18. The apparatus defined in claim 12 wherein said means responsive to said mapping signal comprises:

acousto-optical deflector means.

19. Apparatus for determining whether or not a product has predetermined optically detectable properties including an optically detectable straight line segment in a predetermined object plane comprising:

means for forming a plurality of one-dimensional images of said object plane for said product, each one-dimensional image having a different angle of orientation parallel to said object plane;

means for separately integrating corresponding portions of all of said one-dimensional images to produce a respective projected value for each portion of said integrated one-dimensional images; and

means for analyzing said projected values to determine whether or not said values include a predetermined value that would result if said object plane for said product included said straight line segment.

20. The apparatus defined in claim 19 wherein said means for forming a plurality of one-dimensional images comprises:

a Dove prism mounted for rotation about a rotational axis perpendicular to said object plane for producing an image of said object plane which is rotated by an amount determined by the angle of rotation of said Dove prism about said rotational axis;

means for focusing said rotated image to a one-dimensional image line; and

means for rotating said Dove prism through a predetermined rotational angle to cause said plurality of one-dimensional images to form one after another in succession at said one-dimensional image line.

21. The apparatus defined in claim 19 wherein said means for forming a plurality of one-dimensional images comprises:

means for scanning said object plane to produce an output signal sequentially representative of the intensity of the image at each point in said object plane;

a light source;

means for modulating the intensity of the light from said light source in accordance with said scanning means output signal; and

deflector means for selectively deflecting the modulated light from said light source to selected ones of a plurality of points on a one-dimensional image line based on a predetermined mapping function between the points in said object plane and the points on said one-dimensional image line, said mapping function being a function of the angle of orientation associated with each one-dimensional image.

22. The apparatus defined in claim 19 wherein said means for forming a plurality of one-dimensional images comprises:

computer generated hologram means.

23. Apparatus for determining whether or not a product has predetermined optically detectable properties including an optically detectable straight line segment in a predetermined object plane comprising:

means for forming a plurality of one-dimensional images of said object plane for said product, each one-dimensional image having a different angle of orientation parallel to said object plane, and each one-dimensional image including a plurality of image segments spaced along the longitudinal axis of said one-dimensional image;

means for separately integrating the image segment at each position along the longitudinal axis of a given one-dimensional image with the correspondingly positioned image segments in all of the other one-dimensional images to produce a projected value for each image segment position; and

means for analyzing said projected values to determine whether or not said projected values include a predetermined value that would result if said object plane for said product included said straight line segment.

24. The apparatus defined in claim 23 wherein said means for forming a plurality of one-dimensional images comprises:

a Dove prism mounted for rotation about a rotational axis perpendicular to said object plane for producing an image of said object plane which is rotated by an amount determined by the angle of rotation of said Dove prism about said rotational axis;

means for focusing said rotated image to a one-dimensional image line; and

means for rotating said Dove prism through a predetermined rotational angle to cause said plurality of one-dimensional images to form one after another in succession at said one-dimensional image line.

25. The apparatus defined in claim 24 wherein said means for integrating comprises:

a plurality of photodetectors disposed at said one-dimensional image line, each photodetector detecting an image segment having a respective one of said image segment positions.

26. The apparatus defined in claim 25 wherein said means for integrating further comprises:

means for causing each photodetector to integrate the image segment it receives during rotation of said Dove prism through said predetermined rotational angle.

27. Apparatus for determining whether or not a product has predetermined optically detectable properties including two parallel, optically detectable straight line segments in a predetermined object plane, said straight line segments being spaced from one another by a predetermined perpendicular distance, comprising:

means for forming a plurality of one-dimensional images of said object plane for said product, each one-dimensional image having a different angle of orientation parallel to said object plane, and each one-dimensional image including a plurality of image segments spaced along the longitudinal axis of said one-dimensional image;

means for separately integrating the image segment at each position along the longitudinal axis of a given one-dimensional image with the correspondingly positioned image segments in all of the other one-dimensional images to produce a projected value for each image segment position; and

means for analyzing said projected values to determine whether or not said projected values include two predetermined values separated by a predetermined image segment position difference that would result if said object plane for said product included said two straight line segments.

28. Apparatus for determining whether or not an object plane of a product has predetermined optically detectable properties comprising:

means for detecting the image intensity of a plurality of points in said object plane to produce image intensity data regarding said object plane;

Hough transform means for transforming said image intensity data to Hough array data such that optically detectable straight line segments having a plurality of nonparallel orientations in said object plane are transformed to points in said Hough array data, each possible straight line segment in said object plane being represented in said Hough array data by first, second, and third Hough array coordinates, said first coordinate being representative of the distance of said straight line segment from an origin point in said object plane, said second coordinate being representative of the angle of inclination of said straight line segment in said object plane, and said third coordinate being representative of the amount of optical information in said straight line segment; and

means for analyzing said Hough array data to determine whether or not said Hough array data includes at least one point that would result in said Hough array data if said object plane included said predetermined optically detectable properties, said means for analyzing comprising;

means for projecting said Hough array data parallel to one of said first and second coordinates to produce projected Hough array data; and

means for analyzing said projected Hough array data to determine whether or not said projected Hough array data includes at least one point that would result in said projected Hough array data if said object plane included said predetermined optically detectable properties.

29. The apparatus defined in claim 28 wherein said Hough transform means comprises:

computer generated holograms means.

30. Apparatus for determining whether or not an object plane of a product has predetermined optically detectable properties comprising:

means for detecting the image intensity of a plurality of points in said object plane to produce image intensity data regarding said object plane;

Hough transform means for transforming said image intensity data to Hough array data such that optically detectable straight line segments in said object plane are transformed to points in said Hough array data, each possible straight line segment in said object plane being represented in said Hough array data by first, second, and third Hough array coordinates, said first coordinate being representative of the distance of said straight line segment from an origin point in said object plane, said second coordinate being representative of the angle of inclination of said straight line segment in said object plane, and said third coordinate being representative of the amount of optical information in said straight line segment; and

means for analyzing said Hough array data to determine whether or not said Hough array data includes at least one point that would result in said Hough array data if said object plane included said predetermined optically detectable properties, wherein said object plane has at least one degree of freedom with respect to its positioning relative to said means for detecting, and wherein said means for analyzing comprises;

means for comparing selected portions of said Hough array data to corresponding data for a product which is properly positioned relative to said means for detecting; and

means responsive to said means for comparing for correcting said Hough array data to reverse any effect on said Hough array data due to motion of said product as a result of said at least one degree of freedom.

31. The apparatus defined in claim 30 wherein said Hough transform means comprises:

computer generated hologram means.

32. Apparatus for determining whether or not an object plane of a product has predetermined optically detectable properties comprising:

means for detecting the image intensity of a plurality of points in said object plane to produce image intensity data regarding said object plane, said means for detecting including means for rendering said image intensity data in polar coordinate form;

Hough transform means for transforming said image intensity data to Hough array data such that optically detectable straight line segments in said object plane are transformed to points in said Hough array data, said Hough array data having one angular coordinate; and

means for analyzing said Hough array data to determine whether or not said Hough array data includes at least one point that would result in said Hough array data if said object plane included said predetermined optically detectable properties;

wherein said Hough transform means comprises;

a plurality of light sources each producing light having intensity proportional to said image intensity data at a respective one of a plurality of radius values in said polar coordinate form image intensity data;

a plurality of acousto-optic deflector means;

means for directing light from each of said light sources to a respective one of said acousto-optic deflector means;

means for applying a signal which is a sinusoidal function of said angular coordinate to each of said acousto-optic deflector means;

a plurality of photodetectors; and

means for focusing light from all of said acousto-optic deflector means to said photodetectors.

33. Apparatus for determining whether or not an object plane of a product has predetermined optically detectable properties comprising:

means for detecting the image intensity of a plurality of points in said object plane to produce image intensity data regarding said object plane;

Hough transform means for transforming said image intensity data to Hough array data such that optically detectable straight line segments in said object plane are transformed to points in said Hough array data; and

means for analyzing said Hough array data to determine whether or not said Hough array data includes at least one point that would result in said Hough array data if said object plane included said predetermined optically detectable properties;

wherein said object plane has at least one degree of freedom with respect to its positioning relative to said means for detecting, and wherein said means for analyzing comprises;

means for processing said Hough array data to determine the amount by which said Hough array data is shifted relative to the corresponding data for a product which does not have said at least one degree of freedom;

wherein said means for processing comprises;

a plurality of light sources each of which produced light having intensity proportional to a respective one of a plurality of samples of said Hough array data;

acousto-optic deflector means;

means for applying light from said light sources to said acousto-optic deflector means;

means for applying to said acousto-optic deflector means a signal serially representative of said plurality of samples of said corresponding data;

photodetector means;

means for directing light from said acousto-optic deflector means to said photodetector means; and

means for detecting a maximum in said photodetector means output to indicate a correlation between said samples of said Hough array data and said samples of said corresponding data.

34. The apparatus defined in claim 33 wherein said Hough transform means comprises:

computer generated hologram means.