Patent ID: 8537377

Claim:
An absolute position encoder, comprising: a multi-spectral light source that illuminates a position on a topographic surface at an angle of incidence determined from a vector normal to the surface; a target on, and positionally-registered to, the topographic surface, said target comprising a variable grating that diffracts the incident light to form a multi-spectral diffraction pattern in which the angular dispersion of the diffraction pattern varies with the absolute position of the incident light along the grating; a chromatically responsive sensor that detects a narrow band of the diffraction pattern transmitted through an entrance aperture positioned at an angle of detection determined from the vector normal to the surface and outputs a signal responsive to the change in the angular dispersion of the detected narrow band of the diffraction pattern; and a processing element that maps the detected signal to the absolute-position of illumination by the source on the topographic surface.