Patent ID: 6867412

Claim:
An absolute position sensing device usable to measure a relative position between two elements, the absolute position sensing device including a readhead and a scale, the scale including an integrated scale track extending along a measuring axis, the integrated scale track comprising a plurality of coded segments within the integrated scale track along the measuring axis, each coded segment comprising a periodic portion and a code portion, the periodic portion comprising: a plurality of strip-like first incremental scale elements interleaved with a plurality of strip-like second incremental scale elements along the measuring axis direction, a narrow dimension of the strip-like first and second incremental scale elements extending along the measuring axis direction, at least some of the strip-like first and second incremental scale elements extending to a first edge of the integrated scale track along a direction perpendicular to the measuring axis direction and at least some of the strip-like first and second incremental scale elements extending to an opposite edge of the integrated scale track along the direction perpendicular to the measuring axis direction, wherein the strip-like first incremental scale elements and the strip-like second incremental scale elements are positioned to alternate periodically along the measuring axis direction according to a pitch dimension P, and the code portion comprising: a plurality of code elements defining a code word that is usable to identify a measurement value of a local datum along the measuring axis, the plurality of code elements comprising at least one respective set of respective code elements arranged along the direction perpendicular to the measuring axis direction within a respective code element zone, the respective code element zone located along the measuring axis and extending along the direction perpendicular to the measuring axis direction over at least a part of the width of the integrated scale track, each respective code element having a respective nominal code element dimension along the direction perpendicular to the measuring axis direction that corresponds to respective nominal code element boundaries that extend parallel to the measuring axis direction, wherein: the plurality of first incremental scale elements, the plurality of second incremental scale elements and the plurality of code elements are configured such that a detection window of the readhead includes a number of code elements sufficient to define a code word usable to identify an absolute measurement value of a local datum included in the detection window and at least 50% of a total area of the detection window includes the first incremental scale elements and the second incremental scale elements of at least one periodic portion, regardless of the position of the detection window along the measuring axis of the scale.