Patent ID: 7164145

Claim:
A method for measuring the fiber orientation of a moving web that comprises the steps of: (a) illuminating essentially simultaneously at least four light spots on a first side of the web with at least four plane-polarized incident light beams having different polarization characteristics, wherein each of the at least four plane-polarized light beams is incident substantially perpendicular to the web surface and is transmitted through the web to produce at least four corresponding transmitted excident light spots on a second side of the web that is opposite to the first side; (b) for each of the at least four plane-polarized light beams, measuring the dispersion of the excident light spot along at least one linear section which is at a known angle relative to the plane of polarization of the corresponding plane-polarized incident light beam, wherein at least one such linear section lies substantially across the center of the transmitted excident light spot and extends substantially across the width of the transmitted excident light spot; (c) calculating variations, if any, in the dispersion of the transmitted excident light spot for the at least four plane-polarized light beams; and (d) estimating the fiber orientation of the web from the variations.