Patent ID: 6937349

Claim:
An absolute two-dimensional position sensing device usable to measure a position of a first member with respect to a second member along first and second measuring axes, the absolute two-dimensional position sensing device including a readhead and a scale, the scale including a two-dimensional integrated scale pattern extending along the first and second measuring axes, the two-dimensional integrated scale pattern comprising: a plurality of quasi-random pattern portions, each quasi-random pattern portion extending along the first and second measuring axes and having first and second dimensions, and each quasi-random pattern portion comprising at least a portion of at least one quasi-random pattern; and a plurality of code portions distributed within the two-dimensional integrated scale pattern and spaced apart along a first direction by substantially the first dimension and spaced apart along a second direction by substantially the second dimension, each code portion comprising a plurality of code elements defining at least one code word, the at least one code word usable to identify a measurement value of a local datum along each of the first and second measuring axes; wherein the plurality of quasi-random pattern portions and the plurality of code portions are configured such that a detection window of the readhead that extends along each of the first and second directions includes a number of code elements sufficient to define at least one code word, the defined at least one code word usable to identify the measurement value of a corresponding local datum along the first and second measuring axes, regardless of the position of the detection window within the two-dimensional integrated scale pattern.