Systems and methods for measuring sample surface flatness of continuously moving samples

Abstract

Measurement of sample surface flatness of a continuously moving sample. A conveyor continuously conveys a sample beneath a grating disposed at a non-zero angle with respect to the plane of conveyance. The relative distance between the sample and the angled grating changes with the horizontal translation of the sample. A camera disposed above the sample and the grating captures, at constant time intervals, a sequence of images, each image comprising a shadow moiré fringe pattern that is indicative of the sample's surface flatness. The continuous change in relative distance between the sample and the grating introduces a known or unknown phase step between the shadow moiré fringe patterns of each successive image. A computer associated with the camera processes the images to determine phase values of pixels at, and the relative height of the sample surface at, selected pixel locations of the sample.

1 . A method for measuring surface flatness of a continuously moving sample comprising the steps of:
 conveying the sample on a conveyor surface that extends beneath a grating disposed at a non-zero angle with respect to the plane of conveyance;   capturing a time sequence of images of the sample at different locations beneath the grating using a camera, each image comprising a shadow moiré fringe pattern that is indicative of the surface flatness of the sample;   calculating a lateral offset of the sample, in pixels, between each image acquisition;   in a first of the images, selecting a set of pixel locations in the sample and determining the intensity value at each of the pixel locations;   in each of the other images, selecting the set of pixel locations based on the lateral offset and determining the intensity value at each of the pixel locations;   calculating a phase value for each selected pixel location based on the intensity values; and   calculating a relative height of the sample surface at each pixel location based on the phase values.