Patent ID: 6413702
Filing Date: 2002-07-02
Classification: G01D,G03H

Abstract:
A method for making a encoder, comprising the following steps, in order:(a) generating a mathematical representation of the family of hyperbolic fringes which appear on a plane located a distance d from the midpoint of two coherent point sources a distance p from each other, said representation having an X axis and a Y axis; (b) calculating a apparently constant-pitch curve in said plane of a desired size on which the hyperbolic fringes appear equidistant, the curve intersecting a line normal to the plane containing the point sources and midway between the point sources at a distance d from said midpoint; (c) fabricating a holographic plate into a semicylindrical shape, having a superior and inferior side, the inferior side having the shape of the apparently constant-pitch curve; (d) coating the holographic plate with photosensitive material; (e) disposing the semicylindrical plate the distance, d, from two coherent point sources with the inferior side facing the two coherent point sources, the axis of the semicylindrical holographic plate perpendicular to a line connecting the two coherent point sources so that interference fringes from the two coherent point sources will appear equidistant on the inferior side of the semicylindrical holographic plate, (f) illuminating the holographic plate with the interference fringes produced by the point sources; (g) processing the holographic plate to produce grooves in the plate corresponding to the fringes; and (h) flattening the holographic plate.