Patent ID: 7608813

Claim:
An encoder configuration for use in an absolute position sensing device usable to measure a relative position between two elements along a measuring axis direction, the encoder configuration comprising: an illumination portion; a scale element including an absolute scale pattern comprising a fine track pattern and at least a first absolute track pattern arranged to receive light from the illumination portion and output respective spatially modulated light patterns along respective light paths, each track pattern extending along the measuring axis direction; and a detector electronics comprising a fine track detector portion and at least a first absolute track detector portion arranged in a fixed relationship relative to the illumination portion, and arranged to receive spatially modulated light patterns from the fine track pattern and the first absolute track pattern, respectively, wherein: the first absolute track detector portion comprises individual photodetector areas that have a Y direction edge-to-edge dimension YDETABS 1 along a Y direction that is perpendicular to the measuring axis direction, and the first absolute track detector portion is configured to spatially filter its received spatially modulated light pattern and output a plurality of respective position indicating signals that have respective spatial phases, wherein: the first absolute track pattern comprises geometrically congruent subtrack portions that extend along the measuring axis direction, the geometrically congruent subtrack portions configured such that: the geometrically congruent subtrack portions are separated along the Y direction by a dimension YCENT, and YCENT is less than YDETABS 1 , the geometrically congruent subtrack portions each have a Y direction dimension YTOL, such that the dimensional quantity [YCENT+2(YTOL)] is greater than YDETABS 1 , and the geometrically congruent subtrack portions are arranged such that if one of the geometrically congruent portions is translated along the Y direction by the dimension YDETABS 1 , then the geometrically congruent portions will nominally coincide; and the first absolute track pattern comprises patterned signal varying portions configured such that an area of the patterned signal varying portions varies corresponding to a first periodic function of x having a spatial wavelength L 1 , where x designates an x-coordinate location along the measuring axis direction, and the first periodic function is not a square wave.