Position measuring system with compensation for variable distance between light source and index disk

摘要

A position measuring system with compensation for variable distance between the light source and the index disk. The index disk has a plurality of index lines separated by masked areas. The light source emits beams of light that impinge upon the plane of the index disk at an angle and yet are parallel to the direction of the index lines. The masked areas on the index disk along with the light source positioned at an angle with respect to the axis of the index disk allow the detectors located downstream of the index disk to be maximally illuminated when the index disk is located at its maximum permissible distance from the light source and the detectors are minimally illuminated when the index disk is located at its minimum permissible distance from the light source.