Z-axis optical detection of mechanical feature height

• US 7,747,066 B2
• Filed: 03/15/2006
• Issued: 06/29/2010
• Est. Priority Date: 03/15/2006
• Status: Active Grant

• Current Assignee: X Corp. (f/k/a Twitter, Inc.) (X Holdings Corp.)
• Original Assignee: International Business Machines Corporation
• Inventors: Mulligan, Vincent P.
• Primary Examiner(s): Mehta; Bhavesh M
• Assistant Examiner(s): Thomas; Mia M
• Application Number:
  US11/376,022
• Publication Number:
  US 20070217675A1
• Time in Patent Office: 1,567 Days
• Field of Search: 382141-152, 382168-172
• US Class Current: 382/152
• CPC Class Codes: G01B 11/0608 Height gauges
• CPC Class Codes: G06T 2200/24 involving graphical user interfaces [GUIs]
• CPC Class Codes: G06T 2207/30141 Printed circuit board [PCB]
• CPC Class Codes: G06T 2207/30152 Solder
• CPC Class Codes: G06T 7/0004 Industrial image inspection
• CPC Class Codes: G06T 7/507 from shading G06T7/586 takes precedence
• CPC Class Codes: G06V 10/50 by performing operations within image blocks; by using histograms, e.g. histogram of oriented gradients [HoG]; by summing image-intensity values; Projection analysis
• CPC Class Codes: G06V 10/60 relating to illumination properties, e.g. using a reflectance or lighting model

Abstract

Height attributes of features of an object having a plurality of physical features thereon is determined by illuminating the features of the object at a low angle and capturing the reflected light at a camera mounted along the z-axis perpendicular to the object. The reflected light from the features is analyzed to determine if any of the features is of an unacceptable height. The reflected light being either brighter or dimmer than the average determines that the corresponding feature is higher or lower respectively than the average feature.

Claims

1. A method for detecting heights of a mechanical object, the method comprising the steps of:

creating from an image of the mechanical object, a feature histogram of each of a plurality of selected features of the object, by a processor of a computing device, each selected feature corresponding to one or more of the heights of the mechanical object along an axis perpendicular to a plane of the image of the object, the image captured along the axis, such that the heights of the object are not measured, where the feature histograms of the selected features contain brightness information of the object at the heights of the selected features;

a) calculating a mean value for each of the feature histograms created, by the processor of the computing device;

b) calculating an average value of the plurality of calculated mean values, by the processor of the computing device;

c) determining from the average value, a range of values according to predetermined criteria, by the processor of the computing device;

d) determining whether each calculated mean value is within the range of values, by the processor of the computing device, to determine whether the heights are within a predetermined range without having to measure the heights of the object.

2. The method according to claim 1, comprising the further steps of:

capturing the image of the object with a digital camera; and

transferring the image of the object from the digital camera to an analyzing computer system for performing steps a) through c).

3. The method according to claim 2, comprising the further steps of:

illuminating the object by applying light to the object at an angle less than 20 degrees from a surface of the object;

for capturing the image, placing the digital camera substantially perpendicular to the surface of the object.

4. The method according to claim 3, wherein the applied light is applied from four sides of the object, each light applied placed substantially at 0, 90, 180 and 270 degrees around a perpendicular axis of the surface of the object.

5. The method according to claim 1, comprising the further step of:

prior to the creating the histogram step, enhancing the image wherein the enhancing consists of any one of dilating, erosioning or enhancing contrast.

6. The method according to claim 1, comprising the further steps of:

locating the selected features;

specifying an area of each selected feature to be used in the creating the histogram step wherein the specified area consists of any one of a circle, an oval, a rectangle, or a triangle.

7. The method according to claim 6, wherein the locating step ignores features not to be selected.

8. The method according to claim 1, wherein the feature consists of an electrical contact.

9. The method according to claim 1, comprising the further step of rejecting the object when a predetermined number of features of the object have calculated mean values outside the range of acceptable values.

10. The method according to claim 1, wherein the predetermined criteria is within 30% of the average value.

11. A system for detecting heights of a mechanical object, the system comprising:

a memory;

a computer system in communication with the memory;

a camera in communication with the computer system;

a light source projecting light on features of the object wherein the computer system includes instructions to execute a method comprising;

creating from an image of the mechanical object, a feature histogram of each of a plurality of selected features of the object, each selected feature corresponding to one or more of the heights of the object along an axis perpendicular to a plane of the image of the object, the image captured along the axis, such that the heights of the object are not measured, where the feature histograms of the selected features contain brightness information of the object at the heights of the selected features;

a) calculating a mean value for each of the feature histograms created;

b) calculating an average value of the plurality of calculated mean values;

c) determining from the average value, a range of values according to predetermined criteria;

d) determining whether each calculated mean value is within the range of values, to determine whether the heights are within a predetermined range without having to measure the heights of the object.

12. The system according to claim 11, wherein the system further comprises the steps of:

capturing the image of the object with a digital camera; and

transferring the image of the object from the digital camera to an analyzing computer system for performing steps a) through c).

13. The system according to claim 11, wherein the system further comprises the steps of:

illuminating the object by applying the light to the object at an angle less than 20 degrees from a surface of the object for capturing the image, placing the digital camera substantially perpendicular to the surface of the object.

14. The system according to claim 13, wherein the applied light is applied from four sides of the object, each light applied placed substantially at 0, 90, 180 and 270 degrees around a perpendicular axis of the surface of the object.

15. The system according to claim 11, wherein the system further comprises the steps of:

locating the selected features;

specifying an area of each selected feature to be used in the creating the histogram step wherein the specified area consists of any one of a circle, an oval, a rectangle, or a triangle.

16. A computer-readable storage medium having a computer program stored thereon for execution by processor of a computing device, wherein execution of the computer program by the processor causes a method to be performed, the method for detecting heights of a mechanical object, the method comprising:

creating from an image of the mechanical object, a feature histogram of each of a plurality of selected features of the object, each selected feature corresponding to one or more of the heights of the object along an axis perpendicular to a plane of the image of the object, the image captured along the axis, such that the heights of the object are not measured, where the feature histograms of the selected features contain brightness information of the object at the heights of the selected features;

a) calculating a mean value for each of the feature histograms created;

b) calculating an average value of the plurality of calculated mean values;

c) determining from the average value, a range of values according to predetermined criteria;

d) determining whether each calculated mean value is within the range of values, to determine whether the heights are within a predetermined range without having to measure the heights of the object.

17. The computer-readable storage medium according to claim 16, wherein the method further comprises the steps of:

capturing the image of the object with a digital camera; and

transferring the image of the object from the digital camera to an analyzing computer system for performing steps a) through c).

18. The computer-readable storage medium according to claim 16, wherein the method further comprises the steps of:

illuminating the object by applying light to the object at an angle less than 20 degrees from a surface of the object;

for capturing the image, placing the digital camera substantially perpendicular to the surface of the object.

19. The computer-readable storage medium according to claim 18, wherein the applied light is applied from four sides of the object, each light applied placed substantially at 0, 90, 180 and 270 degrees around a perpendicular axis of the surface of the object.

20. The computer-readable storage medium according to claim 16, wherein the method further comprises the steps of:

locating the selected features;

specifying an area of each selected feature to be used in the creating the histogram step wherein the specified area consists of any one of a circle, an oval, a rectangle, or a triangle.