Optical sensing of a surface.

摘要

To locate the upper surface of an object (18) on a substrate (20), a first real image of a Ronchi ruling (parallel bars) (22) is projected by an objective lens (16) and moved into coincidence with the upper surface by vertical movement of a video camera (10) to which the ruling (22) and lens (16) are fixed. The video camera sensor (12) performs line scanning perpendicular to the bars of a second real image of the ruling (22) formed by the lens (16) projecting light reflected up by the upper surface. Accurate coincidence of the first real image with the upper surface provides a camera output signal containing a strong component at a frequency determined by the spatial frequency of the image scanned and the line scan frequency. Measurement of the vertical position of the camera (10) and sensing of several surface provides signals which can be digitally processed to give data on the structure of, for example, a small manufactured article.