Abstract: This invention relates to a method of operating an absolute encoder apparatus comprising a scale having features defining absolute position information in at least one measuring dimension, and a readhead configured to read the features. The method comprises: obtaining at least one representation of at least some of the features defining absolute position information; analyzing the at least one representation to determine at least one parameter indicative of the quality of the representation; and providing an output indicative of the relative setup of the scale and readhead based at least in part on the at least one parameter.

Abstract: This invention relates to a method of operating an absolute encoder apparatus comprising a scale having features defining absolute position information in at least one measuring dimension, and a readhead configured to read the features. The method comprises: obtaining at least one representation of at least some of the features defining absolute position information; analysing the at least one representation to determine at least one parameter indicative of the quality of the representation; and providing an output indicative of the relative setup of the scale and readhead based at least in part on the at least one parameter.

Abstract: An absolute measurement scale has an incremental scale with light reflecting lines alternating with non-light reflecting lines in which absolute data, in the form of discrete codewords, is embedded in the incremental scale by removing light reflecting lines. The codewords are arranged such that the scale is palindromic and cyclic. A look-up table is used to determine a coarse absolute position by comparing absolute position data extracted from the scale with absolute codewords in the look-up table. The absolute position is determined by combining the coarse absolute position with the position of the start of the first codeword in the data extracted. The absolute position may be determined to within a scale pitch by combining the absolute position with the incremental position.

Abstract: The invention relates to a reference mark detector for use with a metrological scale or encoder (10) having a patterned reference mark rm movable relative to the reference mark detector. The detector may comprise a photodetector array (20) for detecting the patterned reference mark, the array comprising at least two sets of detector elements A and B each set being formed as a pattern which relates to the pattern of the reference mark. The two sets may be separate rows of photodectors or different elements of the same row of photodetectors. The pattern is preferably irregular.

Abstract: A measurement scale (20) is movable in plane x relative to a mask (10) and photodetector (30). When a pattern of apertures in the mask (10) are in correlation with a pattern of apertures e.g. a reference mark in the scale (20) then light bands a b and c may propagate to the detector (30). The relative sizes of the patterns is such that the light bands converge at the detector (30). Other embodiments show light divergent and light inversion correlation of incongruent patterns.

Abstract: An absolute measurement scale 18 comprises an incremental scale 10 with light reflecting lines 12 alternating with non-light reflecting lines 14 in which absolute data, in the form of discrete codewords, is embedded in the incremental scale by removing light reflecting lines 22. The codewords are arranged such that the scale is palindromic and cyclic. A look-up table is used to determine a coarse absolute position by comparing absolute position data extracted from the scale with absolute codewords in the look-up table. The absolute position is determined by combining the coarse absolute position with the position of the start of the first codeword in the data extracted. The absolute position may be determined to within a scale pitch by combining the absolute position with the incremental position.

Abstract: A measurement scale (20) is movable in plane x relative to a mask (10) and photodetector (30). When a pattern of apertures in the mask (10) are in correlation with a pattern of apertures e.g. a reference mark in the scale (20) then light bands a b and c may propagate to the detector (30). The relative sizes of the patterns is such that the light bands converge at the detector (30). Other embodiments show light divergent and light inversion correlation of incongruent patterns.