Optical encoder which use a rectangular photodetector array

Claim 1

In an improved optical encoder having a moveable scale with alternating equally dimensioned opaque and translucent regions extending generally perpendicular to the locus of scale movement; and a light source, a mask and a photodetector array having at least a pair of photodetector areas responsive to light energy from said light source to produce electrical analog signals, said light source, said mask and said array being commonly mounted on a single axis of rotation in a rotatable housing, the mask defining at least two sets of openings with one set being spatially offset from the other set so that a predetermined phase difference is provided between the electrical analog signals put out by the photodetector areas, the improvement comprising: a generally symmetrical, rectangular photodetector array formed with generally rectangular photodetector areas, the major lineal dimensions of said areas being disposed relative to said regions of said scale at a predetermined angle of rotation, each set of said mask defining a series of equally spaced apart elongated openings aligned to be generally parallel with the regions of said scale, said openings being aligned at said angle of rotation relative to said major lineal dimensions of said areas and said openings being sized and arranged to be substantially coextensive with said areas, said housing being rotatable about said axis of rotation so that said phase difference may be bilaterally trimmed to its precise nominal value.