Abstract: A position sensor having a wavefront compensator, a detector array and a grating in a diffractive configuration, and which incorporates a second wavefront compensator and a second detector array in parallel with the first wavefront compensator and detector array, to provide a second optical channel for measurement of an additional degree of freedom (roll), the effects of which can then be removed from or utilized in the main measurement channel; and in which the relative effects of grating roll and grating displacement are different in this second channel when compared to the first sensing channel; and in one embodiment of which this differentiation is created by having different ratios of the grating period to the detector fringe period in the two channels.

Abstract: A position encoder and a method for estimating absolute position using two or more diffractive grating tracks of differing periods to generate interference fringe patterns on a multi-track sensor. Detectors, corresponding to the diffractive grating tracks, detect the interference fringes. A first processing circuitry coupled to the detectors extract phase signals from the signals from the detectors. A second processing circuitry then estimates the cycle counts of the track signals based on the phase signals from the first processing circuitry. The absolute position is estimated by combining the cycle count, the fractional fringe value, and the grating period.