Method and apparatus for on-line determination of fiber orientation and

Abstract

On-line measurement of fiber orientation and anisotropy in a non-woven web of material is performed by directing three light sources toward a sensing region of the web. Reflectively scattered light from each light source is detected by a pair of light sensors positioned on either side of an incidence plane including the beam of incident light. Back scattered light from each light source is also detected by at least one light sensor positioned generally above the sensing region. Preferably two back scattered light sensors are provided for each light source, one common light sensor and one dedicated light sensor. The signals from the light sensors for each of the light sources are combined to generate resultant fiber orientation signals which are used to compute a fiber orientation angle relative to the machine direction and an anisotropy characteristic for the web. The three light sources are modulated and the signals from the light sensors are synchronously demodulated such that light simultaneously incident on the sensing region is electrically separated to correspond to optical paths defined by the three light sources. The resulting signals define points on a generally elliptical polar distribution function of a resultant fiber orientation curve. The curve is approximated by an equation with the measured points being substituted into the equation to form a set of three equations with three unknowns which are then solved to determine the fiber orientation and anisotropy of the web being measured.