Patent ID: 6922254

Claim:
A process for measuring a dimension of an elongated, generally cylindrically-shaped article, comprising: a. illuminating a portion of the article using a light source which casts a beam with nonplanar wavefront onto the article; b. receiving said nonplanar wavefront beam on a light sensor array, the article interposed between the array and the light source so that the beam and the article create a intensity pattern as received by the array, the intensity pattern corresponding to a dimension of the article; c. obtaining from said array a plurality of signals corresponding to light intensity at a plurality of locations in said intensity pattern on said array; and d. determining said dimension by evaluating information from said signals corresponding to light intensity at a plurality of locations in said intensity pattern in accordance with Fresnel diffraction theory, and according to the assumption that the wavefront from the light source is nonplanar; and e. wherein distances between the source, the article and the array are selected such that the intensity pattern in the vicinity of one shadow edge cast by the article on the array is at most negligibly superimposed on the intensity pattern in the vicinity of the other shadow edge cast by the article on the array.