Patent ID: 6781694
Filing Date: 2004-08-24
Classification: G01D

Abstract:
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:at least one periodic portion, each periodic portion extending along the first and second measuring axes, each periodic portion comprising: a plurality of strip-like first periodic scale element zones arranged periodically along a first direction over at least a first range and extending along a second direction over at least a second range, a plurality of the first periodic scale element zones including a characteristic first arrangement of incremental scale features along the second direction, and a plurality of strip-like second periodic scale element zones arranged periodically along the second direction over at least the second range and extending along the first direction over at least the first range, a plurality of the second periodic scale element zones including a characteristic second arrangement of incremental scale features along the first direction; and a plurality of non-periodic portions distributed within the two-dimensional integrated scale pattern and spaced apart along the first direction by at least a first distance that spans at least two first periodic scale element zones including the characteristic first arrangement of incremental scale features along the second direction and spaced apart along the second direction by at least a second distance that spans at least two second periodic scale element zones including the characteristic second arrangement of incremental scale features along the first direction, each non-periodic 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 at least one periodic portion and the plurality of non-periodic 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 the local datum along the first and second measuring axes, regardless of the position of the detection window within the two-dimensional integrated scale pattern.