Patent ID: 6664535
Filing Date: 2003-12-16
Classification: G01D

Abstract:
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 periodic portions placed within the integrated scale track along the measuring axis, each periodic portion comprising a plurality of N consecutive periodic scale elements along the measuring axis, where N is an integer greater than or equal to 3; and a plurality of non-periodic portions placed within the integrated scale track interleaved with the periodic portions along the measuring axis direction of the integrated scale track, each non-periodic 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; wherein the plurality of periodic portions and the plurality of non-periodic portions are configured such that, along the measuring axis direction of the integrated scale track, a detection window of the readhead includes a number of code elements sufficient to define a code word usable to identify the measurement value of the local datum and further includes at least Nâˆ’1 complete periodic scale elements, regardless of the position of the detection window along the measuring axis.