Contamination and defect resistant optical encoder configuration outputting structured illumination to a scale plane for providing displacement signals

A contamination and defect resistant optical encoder configuration for providing displacement signals, comprising:

• a scale that extends along a measuring axis direction, the scale comprising a scale grating comprising grating bars arranged in a scale plane that is nominally parallel to the measuring axis direction, wherein the grating bars are narrow along the measuring axis direction and elongated along a grating bar direction transverse to the measuring axis direction, and are arranged periodically at a scale pitch PSF along the measuring axis direction;
• an illumination source comprising a light source that outputs light, and a structured illumination generating portion configured to input the light and output structured illumination to an illumination region at the scale plane where the structured illumination comprises an illumination fringe pattern comprising fringes that are narrow along the measuring axis direction and elongated along an illumination fringe direction oriented transverse to the measuring axis direction at a nonzero illumination fringe yaw angle relative to the grating bar direction;
• and
• a photodetector configuration comprising a set of N spatial phase detectors arranged periodically at a detector pitch PD along a detected fringe motion direction transverse to the measuring axis direction, wherein each spatial phase detector is configured to provide a respective spatial phase detector signal and at least a majority of the respective spatial phase detectors extend over a relatively longer dimension along the measuring axis direction and are relatively narrow along the detected fringe motion direction transverse to the measuring axis direction, and the set of N spatial phase detectors are arranged in a spatial phase sequence along the detected fringe motion direction;
• wherein:
• the scale grating is configured to input the illumination fringe pattern at the illumination region and output scale light that forms a fringe pattern at the photodetector configuration, the fringe pattern comprising periodic high and low intensity bands that extend over a relatively longer dimension along the measuring axis direction and are relatively narrow and periodic with a detected fringe period PDF along the detected fringe motion direction transverse to the measuring axis direction;
• the detected fringe period PDF and the detected fringe motion direction transverse to the measuring axis direction depend at least partially on the nonzero illumination fringe yaw angle;
• the high and low intensity bands move along the detected fringe motion direction transverse to the measuring axis direction as the scale grating displaces along the measuring axis direction, and
• the photodetector configuration is configured to detect a displacement of the high and low intensity bands along the detected fringe motion direction transverse to the measuring axis direction and provide respective spatial phase displacement signals that are indicative of the scale displacement.