Claims
- 1. A method for inspecting for defects a feature disposed over the surface of a part and which has a predetermined range of heights, said method comprising the steps of providing a camera for imaging said feature, said camera being of the type having an objective lens focussable along a Z-axis and with a predetermined field of view;
providing an autofocus mechanism fixed relative to the camera and for illuminating a selected focus point on, said feature to provide an indication which correlates to the distance along the Z-axis from said lens to said focus points at optimal focus; producing from said indication a focus value for focussing the camera when the camera images the selected focus point.
- 2. The method defined in claim 1 including the step of mapping said surface to define a plurality of focus points including said selected focus point thereon;
moving the mechanism and part relatively so that the mechanism illuminates all of said focus points in succession and provides corresponding distance indications; producing from said distance indications corresponding focus values for all of said focus points; storing all of said focus values as a focus value map, and inspecting the surface for feature defects by moving the camera and part relatively to track the focus value map which focussing the camera at each focus point in accordance with the focus value for that point.
- 3. The method defined in claim 2 including the step of selecting for said camera a CCD camera with optics having a NA of at least 0.05.
- 4. The method defined in claim 2 wherein said surface is mapped so that all of said focus points are on said feature.
- 5. The method defined in claim 1 wherein the mechanism provides the distance indication by
projecting the image of a target onto said feature at said selected point, and moving the lens along the Z-axis until the width of the target image is minimized.
- 6. The method defined in claim 1 wherein the mechanism includes a displacement sensor which measures the actual distance between said lens and said feature at said selected focus point to provide the distance indication.
- 7. A method for inspecting for defects features disposed over the surface of a part and having a predetermined range of heights, said method comprising the steps of providing a camera for optically imaging said features, said camera being of the type having optics including an objective lens focussable along a Z-axis and with a depth of field that is less than said range of heights and a predetermined field of view;
mapping said surface to define a succession of focus points located on said features; projecting an image of a first target through said lens onto said surface so that the first target image remains in said field of view; moving the camera and part relatively to track the succession of focus points; at each focus point, moving the lens along the Z-axis until the width of the first target image as seen by the camera is minimized to provide an indication of the distance from the lens to the feature that achieves optimal focus, and producing a focus value corresponding the distance indication for each focus point; storing all of the focus values as a focus value map.
- 8. The method defined in claim 7 including the additional step of performing an inspection by moving the camera and part relatively to track the focus value map while focussing the camera lens at each focus point in accordance with the focus value for that point.
- 9. The method defined in claim 7 including the additional step of selecting for the camera a CCD camera with optics having a NA of at least 0.05.
- 10. The method defined in claim 7 including the additional step of
projecting an image of a second target off the Z-axis onto said surface, the lateral position of the second target in said field of view relative to the first target image indicating the magnitude and direction of the movement of said lens along the Z-axis, the distance indication for optimal focus at each focus point being provided when the image of the second target is superimposed on the first target image having minimum width.
- 11. The method defined in claim 10 including the additional step of selecting for the camera a CCD camera with optics having a NA of at least 0.05.
- 12. A method for inspecting for defects features disposed over the surface of a part and having a predetermined range of heights, said method comprising the steps of
providing a camera for optically imaging said features, said camera being of the type having optics including an objective lens focussable along a Z-axis and with a depth of field that is less than said range of heights and predetermined field of view; mapping said surface to define a succession of focus points on said features; moving the camera and part relatively to track the succession of focus points at each focus point, determining the distance between said lens and the feature at that point to produce a distance indication; generating focus values corresponding to the distance indications and storing the focus values as a focus map.
- 13. The method defined in claim 12 including the additional step of performing an inspection by moving the camera and part relatively to track the focus map while focusing the camera lens at each focus point in accordance with the focus value for that point.
- 14. The method defined in claim 13 including the additional step of selecting for the camera a CCD camera with optics having a NA of at least 0.05.
- 15. A method for inspecting for defects a feature disposed as one or more strips over the surface of a part and having a predetermined range of heights, said method comprising the steps of
providing a camera for optically imaging said feature, said camera being of the type having optics including an objective lens focussable along a Z-axis and with a depth of field that is less than said range of heights and a predetermined field of view; providing a displacement sensor fixed relative to said camera and for illuminating a succession of focus points on at least one of said strips to provide at each focus point on indication which correlates to the distance along the Z-axis from said lens to that focus point; producing from each indication a focus value for focussing the camera lens when the camera images the corresponding focus point and storing that focus value; moving the part relative to the camera and displacement sensor in a scan direction so that the displacement sensor illuminates a leading focus point in the succession of focus points while the camera is imaging a trailing focus point in said succession of focus points, and whereby the focus value for each focus point in the succession of focus points is produced in spatial and temporal advance of the imaging by the camera requiring that focus value.
- 16. The method defined in claim 15 and including the additional step of selecting for the camera a CCD camera with optics having a NA of at least 0.05.
- 17. The method defined in claim 15 wherein the leading and trailing focus points are on one strip.
- 18. The method defined in claim 15 the feature includes at least two strips spaced side by side, and
the leading focus point is on one strip and the trailing focus point is on the other strip.
- 19. The method defined in claim 15 including the step of positioning the camera and displacement sensor relatively so that the displacement sensor is ahead of the camera in the scan direction.
- 20. The method defined in claim 15 including the steps of
forming said feature as side by side strips, and positioning the camera and displacement relatively so that the displacement sensor is aimed laterally to the scan direction so that the displacement sensor illuminates one strip while the camera images the other strip whereby the focus value for the focus points on one strip can be produced and stored in advance of the imaging of the one strip by the camera requiring those focus values and while the camera is imaging the other strip.
- 21. The method defined in claim 15 including the steps of
forming an image of the part surface of fluorescent material; selecting a displacement sensor which projects an illumination pattern of a first frequency that excites fluorescent emission of a second frequency from said surface and which filters out the first frequency so that only light of the second frequency provides said distance indication.
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of Provisional Application No. 60/433,817 filed Dec. 16, 2002.
Provisional Applications (1)
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Number |
Date |
Country |
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60433817 |
Dec 2002 |
US |