Computer aided inspection machine

• US 6,064,759 A
• Filed: 11/06/1997
• Issued: 05/16/2000
• Est. Priority Date: 11/08/1996
• Status: Expired due to Fees

• Current Assignee: Buckley B. Shawn, Dao Shan Yang, Hui Cheng Zhou, Jihong Chen
• Original Assignee: Buckley B. Shawn, Dao Shan Yang, Hui Cheng Zhou, Jihong Chen
• Inventors: Chen, Jihong, Buckley, B. Shawn, Zhou, Hui Cheng, Yang, Dao Shan
• Primary Examiner(s): Boudreau, Leo H.
• Assistant Examiner(s): MEHTA, BHAVESH M
• Application Number:
  US08/965,542
• Time in Patent Office: 922 Days
• Field of Search: 382/106, 382/141, 382/154, 382/199, 382/203, 382/285, 382/286, 382/149, 382/151, 382/108, 356/376, 345/419, 345/425, 348/86-87, 348/94-95, 348/125-130, 250/559.22, 250/559.23
• US Class Current: 382/154
• CPC Class Codes: G01B 11/024 by means of diode-array scanning

Abstract

An automatic inspection method and apparatus using structured light and machine vision cameras to inspect an object in conjunction with the geometric model of the object is disclosed. Camera images of the object are analyzed by computer to produce the location of points on the object'"'"'s surfaces in three dimensions. During a setup phase before object inspection, the points are analyzed with respect to the geometric model computer file of the object. Many points are eliminated to reduce data-taking and analysis time to a minimum and to prevent extraneous reflections from producing errors. When similar objects are subsequently inspected, points from each surface of interest are spatially averaged to give high accuracy measurements of object dimensions. The inspection device uses several multiplexed sensors, each composed of a camera and a structured light source, to measure all sides of the object on a single pass. Calibration and compensation methods are also disclosed.

Claims

1. A system for measuring the shape characteristics of a plurality of objects comprising:

a first object having a plurality of locations on a plurality of surfaces to be inspected;

a structured light source disposed at a first angle to illuminate said first object;

a camera disposed at a second angle from said first angle such that the locations on the surfaces of said first object can be found in three dimensional space, said camera adapted to create an image from light reflected from said first object;

an array of light gathering elements for gathering the imaged light from said camera and converting said imaged light into an electrical signal;

analysis means adapted to determine shape characteristics by dividing the image of the object into a multiplicity of simplified surface primitives and edge primitives and finding a set of three dimensional locations on each contributing primitive; and

inspection means by which the same shape characteristics of a plurality of subsequent objects are determined;

wherein, a plurality of objects are inspected by illuminating said first object with said structured light source, creating an image of said first object with said camera, converting the image into an electrical signal with said array of light gathering elements, analyzing the signal with the analysis means, repeating the process for each of said subsequent objects, and comparing results with results from said first object.

2. The system of claim 1 wherein the surface primitives of said analysis means are chosen from a group consisting of planes, cylinders, cones, helixes, Torii and spheres.

3. The system of claim 1 in which the edge primitives of said analysis means are chosen from a group consisting of straight lines, arcs, conic sections and space curves.

4. The system of claim 1 wherein the set of three dimensional locations includes only those three dimensional locations that are in close proximity to a surface primitive.

5. The system of claim 1 wherein the set of three dimensional locations includes only those three dimensional locations that produce similar electrical signals at different times while the object remains stationary.

6. The system of claim 1 wherein the set of three-dimensional locations includes only those three dimensional locations that are surrounded by other three dimensional locations at approximately the same position in three-dimensional.

7. The system of claim 1 wherein said inspection means uses a difference in the electrical signals between said first object and subsequent objects to determine shape characteristic differences between said first object and subsequent objects.

8. The system of claim 1 wherein a repeatability of said inspection means may be improved by increasing a number of three dimensional locations in said set of three dimensional locations.

9. The system of claim 1 wherein a number of locations in the set of three-dimensional locations is pruned to minimize a time required to inspect the object.

10. The system of claim 1 wherein said analysis means determines a location, a shape and an orientation of each surface primitive and each edge primitive based upon the set of three dimensional locations found on said first object;

defines a set of parameters that specify an idealized set of primitives; and

compares three dimensional locations found on subsequent objects to the idealized set of primitives.

11. The system of claim 10 wherein said analysis means detects flaws in subsequent object by comparing each three dimensional location associated with a primitive of a subsequent object to a corresponding location computed from its idealized primitive to determine the position and size of the flaw.

12. The system of claim 10 wherein said analysis means detects changes in dimensions of a subsequent object with respect to said first object by comparing a parameter set of a primitive of said first object with a parameter set of the corresponding primitive of the subsequent object.

13. The system of claim 10 wherein said analysis means performs a least squares fit of the three dimensional locations associated with each primitive of subsequent objects to the corresponding idealized primitive to determine changes in location, shape and orientation of that primitive with respect to said first object.

14. The system of claim 10 wherein said analysis means adjusts location, shape and orientation of the idealized primitives found from three dimensional locations of said first object based upon information provided during a setup phase by a user of said system.

15. The system of claim 1 wherein said structured light source is a laser light source.

16. The system of claim 15 wherein the laser light source comprises optical mechanisms that focus the light into a laser light plane having a narrow thickness relative to a size of said object, and a scanner for moving the laser light plane relative to the first and subsequent objects to illuminate a narrow portion of said first object and subsequent objects.

17. The system of claim 16 wherein the scanner moves the objects past a stationary laser light plane.

18. The system of claim 16 wherein the scanner directs the laser light plane onto a mirrored surface that rotates about an axis to move the laser light plane over a stationary object.

19. The system of claim 16 wherein an intensity of the laser is controlled as the plane moves over said objects to maintain a substantially constant light intensity imaged by said camera.

20. The system of claim 15 wherein said laser light source comprises optical mechanisms that focus the light into a laser light spot having a size that is small compared to the size of object surfaces, and a scanning mechanism for moving the laser light spot relative to the first and subsequent objects to illuminate a small spot on said first object and subsequent objects.

21. The system of claim 20 wherein the scanning mechanism directs the laser light spot onto two successive mirrored surfaces rotating about an axis in order to move the laser light spot over a stationary object.

22. The system of claim 20 wherein an intensity of the laser producing the light spot is controlled as the spot moves over said objects to maintain a substantially constant light intensity imaged by said camera means.

23. The system of claim 1 further comprising a rotating fixture for positioning said objects such that shape characteristics on two or more sides of said objects may be determined.

24. The system of claim 1 wherein said analysis means and said inspection means use the spatial average of a multiplicity of first objects all positioned at approximately the same location and orientation for finding the set of three dimensional locations on contributing primitives.

25. The system of claim 1 further comprising mirrored surfaces that reflect structured light from said light source onto primitives of the object that are occluded from illumination by a straight path from the light source and in which reflected light from the same primitives are reflected by the mirrored surfaces for imaging onto the array of light gathering elements.

26. The system of claim 1 wherein a multiplicity of cameras image light reflected from different sides of said first object and wherein said analysis means uses a set of three dimensional locations found by the multiplicity of camera means on said first object to determine the shape characteristics of subsequent objects by analyzing the electrical signals of the multiplicity of camera means at the locations found for said first object.

27. The system of claim 1 wherein said analysis means further comprises a set of editing tools, said editing tools allowing a user to identify primitives by editing a graphical representation of said first object.

28. The system of claim 27 wherein said set of editing tools comprises at least one tool selected from a group consisting of tools for identifying primitives by identifying one or more three dimensional locations in the primitive, tools for eliminating three dimensional locations which lie further than a statistically determined distance from a primitive, tools for to determining the extent of a primitive, tools for partitioning primitives into several primitives, tools for joining several primitives into a single primitive, tools for adjusting primitives to position them relative to other primitives and to reference surfaces, and tools for specifying the primitives to be used for the determination of shape characteristics of subsequent objects.

29. The system of claim 1 wherein said analysis means is adapted to allow primitives to be fixed in orientation but repositioned by least squares fit to a position that more closely matches the three dimensional locations found on a subsequent object in order to more accurately determine shape characteristics of that object.

30. A system for measuring shape characteristics of an object comprising:

a first object having a plurality of surfaces having a plurality of shapes to be inspected;

a desired object having a plurality of surfaces and a plurality of surfaces specified by a computer file;

a structured light source disposed at a first angle to illuminate said first object;

a camera disposed at a second angle from said first angle such that the locations on the surfaces of said first object can be found in three dimensional space, said camera adapted to create an image from light reflected from said first object;

an array of light gathering elements for gathering the imaged light from said camera and converting said imaged light into an electrical signal;

simulation means for simulating optical characteristics and electrical characteristics of said structured light source and said camera in three dimensions, dimensions and orientation of a layout of the system, and light reflection characteristics of the desired object to simulate the electrical output of each element of said array of light gathering elements by said desired object when illuminated by said light source;

analysis means adapted for determining shape characteristics by dividing said desired object into a multiplicity of simplified surface and edge primitives and using said simulation means to predict a set of three dimensional locations on each primitive;

inspection means by which the shape characteristics of objects having a similar shape to the shape of the desired object in said computer file are determined by positioning the similar object at approximately the same location and orientation as the simulation of said desired object and analyzing the electrical signals of the camera means at the three dimensional locations found from said analysis means.

31. The system as claimed in claim 30 wherein said simulation means is further adapted to calculate a differential variation of simulated system parameters with respect to actual measurements of three dimensional surface locations of said first object.

32. The system as claimed in claim 30 wherein a set of three-dimensional locations of said first object includes only those three-dimensional locations that are in close proximity to a surface primitive.

33. The system as claimed in claim 30 wherein a set of three-dimensional locations of said first object includes only those three dimensional locations that produce similar electrical signals at different times while the object remains stationary.

34. The system as claimed in claim 30 wherein a set of three-dimensional locations of said first object includes only those three dimensional locations that are surrounded by other three dimensional locations at approximately the same position in three-dimensional space.

35. The system as claimed in claim 30 wherein said inspection means determines differences in shape characterics between said desired object and said first object by comparing the difference between the actual electrical signals from said first object and simulated electrical signals for the desired object.

36. The system as claimed in claim 30 wherein a repeatability of said inspection means may be improved by increasing a number of three-dimensional locations in said set of three-dimensional locations.

37. The system as claimed in claim 30 wherein a number of locations in the set of three-dimensional locations is pruned to minimize a time required to inspect the object.

38. The system as claimed in claim 30 wherein said analysis means detects flaws in subsequent object by comparing each three dimensional location associated with a primitive of a subsequent object to a corresponding location computed from its idealized primitive to determine the position and size of the flaw.

39. The system as claimed in claim 30 wherein said analysis means detects changes in dimensions of a subsequent object with respect to said first object by comparing a parameter set of a primitive of said first object with a parameter set of the corresponding primitive of the desired object.

40. The system as claimed in claim 30 wherein a set of three dimensional locations associated with each primitive of objects having a similar shape to the desired object is least squares fit to a corresponding primitive of said desired object to determine changes in location, shape and orientation of that primitive with respect to said desired object.

41. The system as claimed in claim 30 wherein said structured light source is a laser light source.

42. The system as claimed in claim 30 wherein the laser light source comprises optical mechanisms that focus the light into a laser light plane having a narrow thickness relative to a size of said first object, and a scanner for moving the laser light plane relative to the first objects to illuminate a narrow portion of said first object.

43. The system as claimed in claim 42 wherein said scanner moves said first object past a stationary laser light plane.

44. The system as claimed in claim 42 in which the scanning mechanism directs the laser light plane onto a mirrored surface which rotates about an axis to move the laser light plane over a stationary object similar to the desired object.

45. The system as claimed in claim 44 wherein the scanner directs the laser light spot onto two successive mirrored surfaces, each rotating about an axis, to move the laser light spot over stationary objects similar to said desired object.

46. The system of claim 30 wherein said desired object is positioned on a simulated rotating fixture and said first object is positioned on an actual rotating fixture to allow determination of shape characteristics on two or more sides of the object;

and

whereby a shape characteristics associated with a primitive which is occluded from view on one side of the object can be determined using three-dimensional locations found on another side of the object.

47. The system as claimed in claim 30 wherein said simulation means further comprises error correction means for the optical and electrical characteristics of said structured light source and said camera means, for the mechanical operation of scanning mechanisms, for the dimensions and orientation of the system layout and for the light reflection characteristics of the desired object based upon actual measurements made by said inspection means on an object having known shape characteristics;

whereby the error correction means are such that the simulated shape characteristics of the desired object asymptotically approach the known shape characteristics of the measured object as the error correction means become more refined.

48. The system as claimed in claim 47 wherein error correction means are adapted to perform a sensitivity analysis of a set of system parameters to a set of measured errors between desired object shape characteristics and known object shape characteristics in which the set of parameters is least squares fit to the set of measured errors.

49. The system as claimed in claim 30 wherein a multiplicity of cameras image simulated reflected light from different sides of said desired object and wherein said analysis means uses a set of three dimensional locations found by the multiplicity of cameras on said desired object;

wherein said inspection means determines the shape characteristics of similar objects by analyzing the electrical signals of the multiplicity of camera means at the locations found for said desired object.

50. The system of claim 30 wherein said analysis means further comprises a set of editing tools, said editing tools allowing a user to identify primitives by editing a graphical representation of said desired object.

51. The system as claimed in claim 50 wherein said editing tools include ways to identify primitives by identifying one or more three dimensional locations in the primitive, ways to eliminate three dimensional locations which lie further than a statistically determined distance from a primitive, ways to determine the extent of a primitive, ways to partition or ungroup primitives into several primitives, ways to join or group several primitives into a single primitive, ways of adjusting primitives to position or align them with other primitives or with reference surfaces and ways of specifying the primitives to be used for the determination of shape characteristics of similar objects.

52. The system of claim 30 wherein said analysis means is adapted to allow primitives to be fixed in orientation but repositioned by least squares fit to a position that more closely matches the three dimensional locations found on said first object in order to more accurately determine shape characteristics of said first object.