Method for determining localized fiber angle in a three dimensional

Abstract

The invention is a method for measuring fiber angle in a fibrous solid material relative to three mutually orthogonal reference axes. It is particularly well suited for measuring diving grain and grain surface angle in wood. The method is based on the measurement of the intensity of reflected light at different azimuthal angles when a beam of light of small diameter is impinged upon the surface. The nature of the specular reflections from a light beam striking the surface of a cylinder serves as a model for the system. A preferred apparatus for practicing the method comprises a light source, which may be a low powered laser, aimed normal to the surface of the fibrous material. A plurality of photosensors lying in a plane normal to the axis of the light beam are placed around the light source to detect the light reflected at various azimuthal angles. When the fibers of the material lie normal to the light beam, reflected light maxima are seen 180.degree. apart at positions normal to the longitudinal axis of the fibers. If the fiber axes in the material are tilted out of normalcy with respect to the incoming light beam, even though the surface of the material is normal, the azimuthal angle between the reflected light maxima decreases as a function of the tilt angle. Various alternative methods include the use of an on-axis photosensor with a multiplexed series of light sources arranged around the axis. These lights may be used simultaneously if they are of different wavelengths and the photosensor employs a beam splitting and filtering system sensitive to each different light source.