Patent ID: 7423754

Claim:
An apparatus for measuring web planarity, comprising: a reflective reference surface lying in a horizontal plane; a light source adapted to project a light pattern onto the reference surface along a non-vertical axis, said light pattern having discrete regions that intercept the reference surface; a support adapted to receive a web and to bear the received web vertically offset from the reference surface such that the received web intercepts the discrete regions of the projected light pattern; and an imaging device adapted to: detect (1) positions on the reference surface of interception of the discrete regions of the projected light pattern and (2) respective positions on the received web of interception of the same discrete regions of the projected light pattern, determine the vertical offset of the respective positions on the received web as a function of differences in the detected positions on the reference surface and the respective detected positions on the received web, and calculate a measure of non-planarity of the received web based upon a comparison of a plurality of such vertical offsets from a plurality of detected positions of the received web.