Patent ID: 7015445

Claim:
A method for inspecting for defects of 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.