Patent ID: 8604413

Claim:
A displacement sensor configuration, comprising: a scale grating including grating bars disposed in a first direction, each of the grating bars extending in a second direction that is substantially perpendicular to the first direction and the scale grating defining a set of diffraction planes corresponding to a set of diffractive order angles corresponding to a hypothetical plane wave perpendicularly incident onto the scale grating, and a scale light imaging configuration, including: an illumination portion configured to provide illumination light to the scale grating, the hypothetical plane wave and the illumination light having the same wavelength, an imaging configuration including first and second optical paths, and a detector including first and second detector portions, wherein: the displacement sensor configuration is configured to output a first scale light component from the scale grating to the imaging configuration and along the first optical path which is configured to output the first scale light component to the first detector portion, the displacement sensor configuration is configured to output a second scale light component from the scale grating to the imaging configuration and along the second optical path which is configured to output the second scale light component to the second detector portion, and proximate to the scale grating the second optical path is inclined at an angle relative to a direction normal to the scale grating, the angle defined in a plane including the direction normal to the scale grating and the first direction, the first detector portion is configured to receive the first scale light component transmitted along the first optical path and output a first displacement signal that includes at least a first signal component indicative of a displacement of the scale light imaging configuration relative to the scale grating along the first direction, and the second detector portion is configured to receive the second scale light component transmitted along the second optical path and output a second displacement signal that includes the first signal component and a second signal component indicative of a displacement of the scale light imaging configuration relative to the scale grating along a third direction that is perpendicular to the first and second directions.