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

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, the sample comprising a discrete object;
• 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;
• in each of the images, determining the intensity value of each pixel;
• calculating a lateral offset of the sample, in pixels, between each image acquisition;
• for each pixel, calculating a brightness value based on the intensity value of the pixel in each image and the lateral offset;
• assembling a brightness image from the brightness values;
• applying an optical part location algorithm to locate the sample within the brightness image;
• responsive to the results of the optical part location algorithm, in a first image of the sequence of the images, selecting a set of pixel locations in the sample;
• in each of the other images of the sequence of images, selecting the set of pixel locations based on the lateral offset;
• 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.

A system for measuring surface flatness of a continuously moving sample comprising:

• a conveyor continuously conveying a sample along a plane of conveyance;
• a grating disposed above the sample at a non-zero angle with respect to the plane of conveyance;
• a light source configured to illuminate the grating and the sample;
• a camera disposed above the grating and the sample and configured to capture at least one image comprising a shadow moiré fringe pattern that is indicative of the surface flatness of the sample;
• and
• a computer associated with the camera and configured to process the image to measure the surface flatness of the sample.