Apparatus for measuring diagonal and simplex paper curl

摘要

A method and apparatus for measuring the curl in a vertically suspended sheet of paper is disclosed. A pair of spaced horizontal laser beams is directed through a pair of collimating lenses to produce laser beams having a given width. The collimated beams are directed against the upper and lower side edges of the sheet in a direction parallel with the planar face of the sheet. The shadow images cast from the interruption of the pair of beams by the upper and lower edges of the sheet are detected and compared, with the difference between the images corresponding with the diagonal curl of the paper sheet.