Optical encoder having an optical portion comprising dual lenses and an aperture portion positioned in relation to a moiré grating

Abstract

An optical encoder comprises an illumination source, a scale grating extending along a measuring axis direction, an optical portion, a moiré grating, and a detector portion. The optical portion comprises an aperture portion for spatial filtering of scale light from the scale grating. The moiré grating is configured to receive the spatially filtered scale light and output a spatially modulated fringe pattern toward the detector portion. The optical portion outputs the spatially modulated scale light to form a primary interference fringe pattern with a primary fringe pitch P. The detector portion comprises at least N respective detector elements positioned to detect N respective spatial phases of the periodic spatially modulated fringe pattern, where N is an integer that is at least three, and each respective detector element has a width dimension DW that is at least as large the primary fringe pitch Palong a direction of the fringe displacement.