Apparatus for determining the parameters of figures on a surface

• US 4,379,308 A
• Filed: 12/28/1981
• Issued: 04/05/1983
• Est. Priority Date: 02/25/1980
• Status: Expired due to Fees

• Current Assignee: BMC Industries Incorporated National Bank Building St Paul Minnesota 55101
• Original Assignee: Cooper Industries, Inc. (Eaton Corporation PLC.)
• Inventors: Kosmowski, Wojciech, Eddy, Richard, O'Neill, Martin
• Primary Examiner(s): BRITTON, HOWARD W
• Application Number:
  US06/335,097
• Time in Patent Office: 463 Days
• Field of Search: 358/101, 358/106, 358/107, 364/515, 356/394
• US Class Current: 348/126
• CPC Class Codes: G01B 11/024 by means of diode-array scanning

Abstract

The disclosed apparatus determines the parameters, such as size, shape, and position, of figures on a surface. It includes a camera means generating a video signal. A table assembly adjusts the position of the camera and surface on the table with respect to each other as specified by position signals. Control circuitry generates the position signals so as to bring at least a portion of a figure into the camera'"'"'s field of view. The video signal generated when this portion of a figure is in view is used by processing circuitry to determine the figure'"'"'s parameters.

In one embodiment, the expected parameter values for a figure are retrieved from storage circuitry and compared against the parameter values as determined by the processing circuitry. If the parameter values are out of range, an error signal is generated. Error data may be recorded or transmitted to an external device for statistical analysis.

Claims

1. An inspection apparatus for determining parameters of a generally circular figure on a surface, comprising:

camera means for generating a video signal representative of the field of view before said camera means;

table means for supporting said camera means and said surface in an adjustable spaced position with respect to each other such that selected portions of said surface may be brought within said field of view, said table means accepting position signals to adjust said spaced position;

control means for generating position signals to bring at least a portion of said figure within said field of view and for supplying said position signals to said table means;

digitizer circuitry generating from said camera means video signal an associated digital signal which discriminates between portions of said video signal representing a portion of said figure within said field of view and other portions of said video signal;

sampling means for sampling said digital signal to determine associated values for a grid of picture elements, each said picture element corresponding to a fixed portion of said field of view and having a value indicating whether said corresponding fixed portion of said field of view includes a portion of said figure;

addressable storage means for storage and retrieval of said picture element values; and

processing means, accessing said storage means, for determining the size and position of said figure from said picture element values associated with the video signal generated when said figure is entirely within said field of view of said camera means,

wherein said processing means includes means for accessing said storage means to locate first and second boundary picture elements in a grid column, each representing distinct boundary portions of said figure;

means for locating a midpoint picture element in the grid midway between said first and second boundary picture elements;

means for accessing a third boundary picture element in the same grid row as said midpoint picture element, representing another distinct portion of said figure; and

means for determining the size and center of said figure from the grid addresses of said three boundary picture elements.

2. An apparatus according to claim 1 wherein said table means includes:

a first guide rail;

a table supporting said surface and controllably slidable on said first guide rail along a first line;

a second guide rail disposed in a fixed position above and perpendicular to said first guide rail;

a carriage controllably slidable on said second guide rail along a second line; and

a focusing means attached to said carriage and to which said camera means is attached, for controllably moving said camera means along a third line generally perpendicular to said second line to bring a portion of said surface within said field of view into focus.

3. An apparatus according to claim 1 further comprising:

storage means for storage and retrieval of expected size and position values for said figure; and

verification means, coupled to said storage means and to said processing means, for comparing the determined size and position values of said figure against the expected values, and for generating a defect signal indicative of the results of said comparison.

4. An apparatus according to claim 1 wherein said processing means, in order to determine the center of said figure, further comprises:

means for determining the perpendicular bisector of the line between said first and third boundary picture elements;

means for determining the perpendicular bisector of the line between said second and third boundary picture elements;

means for determining the grid intersections of said perpendicular bisectors with the line between said third boundary picture element and said midpoint picture element; and

means for locating a center picture element in the grid midway between said intersections.

5. An apparatus according to claim 1, further comprising:

focusing means for adjusting the position of said camera means and surface with respect to each other to bring the portion of said surface in said field of view into focus.

6. An apparatus according to claim 5 wherein said focusing means is configured to separate said camera means and said surface by a predetermined focus distance.

7. An apparatus according to claim 1 further comprising illumination means for illuminating said camera means field of view.

8. An apparatus according to claim 7 wherein said illumination means comprises:

a coaxial light supply, projecting light of controllable intensity in a direction generally perpendicular to said surface;

an off-axis light supply, projecting light of controllable intensity in directions not generally perpendicular to said surface; and

mixing means for controlling the intensity of light generated by said coaxial and said off-axis light supplies to improve the contrast of said figure with respect to said surface.

9. An inspection apparatus for determining the size and position of generally circular holes in a printed circuit board, comprising:

first digital storage means for storage and retrieval of expected hole locations and sizes;

camera means for generating a video signal representative of the field of view before said camera means;

control means for accessing said first digital storage means to recall at least one of said expected hole locations, and for generating position signals indicating a portion of the printed circuit board corresponding to a recalled expected hole location;

table means, supporting said camera means and the printed circuit board in an adjustable spaced position with respect to each other, for accepting said position signals to adjust said spaced position of the printed circuit board to locate the expected hole location within the field of view of said camera means;

video digitizing means for converting said video signal into a corresponding grid of digital picture elements, each corresponding to a fixed portion of said field of view, and each having a value indicating whether the corresponding fixed portion of said field of view includes a portion of a located hole;

second digital storage means for storage and retrieval of said picture element values; and

processing means, accessing said second digital storage means and coupled to said control means, for determining the size and position of a located hole from said position signals and from said picture element values associated with the video signal generated when said hole is entirely within the field of view of said camera means;

verification means, coupled to said first digital storage means and to said processing means, for comparing the determined size and position values of a located hole against the expected values, and for generating an error signal indicative of the results of said comparison.

10. A printed circuit board inspection apparatus according to claim 9, wherein said processing means includes means for accessing said second digital storage means to locate first and second boundary picture elements in a grid column, each representing distinct boundary portions of a located hole;

means for locating a midpoint picture element in the grid midway between said first and second boundary picture elements;

means for accessing a third boundary picture element in the same grid row as said midpoint picture element, representing another distinct portion of a located hole; and

means for determining the size and center of a located hole from the grid addresses of said three boundary picture elements.

11. A printed circuit board inspection apparatus according to claim 10, wherein said processing means, in order to determine the center of a located hole, further comprises:

means for determining the perpendicular bisector of the line between said first and third boundary picture elements;

means for determining the perpendicular bisector of the line between said second and third boundary picture elements;

means for determining the grid intersections of said perpendicular bisectors with the line between said third boundary picture element and said midpoint picture element; and

means for locating a center picture element in the grid midway between said intersections.