A contamination and defect resistant rotary optical encoder configuration for providing displacement signals, including at least a first measurement channel comprising:
- a rotary scale that extends along a rotary measuring direction about a rotary axis that is perpendicular to a rotary plane, the rotary scale comprising a rotary scale grating comprising scale grating bars arranged on a rotary surface that extends along the rotary measuring direction, wherein the scale grating bars are narrow along the rotary measuring direction and elongated along a rotary scale grating bar direction transverse to the rotary measuring direction, and are arranged periodically at a nominal scale pitch PSF along the rotary measuring direction;
- an illumination source comprising a light source that outputs source light to a structured illumination generating arrangement, the structured illumination generating arrangement comprising a first illumination region on the rotary scale, a beam deflector configuration comprising at least first and second deflector elements, and a second illumination region on the rotary scale, wherein the structured illumination generating arrangement is configured to input the source light to the first illumination region which diffracts and outputs the source light as structured illumination light to the beam deflector configuration, which is configured to cause diffracted beams of the structured illumination light to cross over one another and transmit the resulting structured illumination light to the second illumination region on the rotary scale and form an illumination fringe pattern proximate to the second illumination region, the illumination fringe pattern comprising fringes that are narrow along the rotary measuring direction and elongated along an illumination fringe direction oriented transverse to the rotary measuring direction;
- and
- a detector arrangement including a photodetector configuration comprising a set of N spatial phase detectors arranged periodically at a detector pitch PD along a detected fringe motion direction that is transverse to the rotary measuring 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 rotary measuring direction and are relatively narrow along the detected fringe motion direction transverse to the rotary measuring direction, and the set of N spatial phase detectors are arranged in a spatial phase sequence along the detected fringe motion direction;
- wherein:
- the rotary scale grating bar direction is oriented at a nonzero yaw angle ψ on the rotary surface relative to a direction perpendicular to the measuring axis direction and along the rotary surface;
- the structured illumination generating arrangement is configured such that the illumination fringe direction of the illumination fringe pattern proximate to the second illumination region on the rotary scale is oriented at a nominal fringe direction yaw angle that is rotated by a non-zero yaw difference angle YDA relative to the scale grating bar direction proximate to the second illumination region on the rotary scale;
- the rotary scale grating is configured to input the illumination fringe pattern at the second illumination region and output scale light that forms a periodic scale light pattern comprising a detector fringe pattern at the photodetector configuration, the detector fringe pattern comprising periodic high and low intensity bands that extend over a relatively longer dimension along a direction parallel to the rotary measuring direction and are relatively narrow and periodic with a detected fringe period PDF along the detected fringe motion direction transverse to the rotary measuring direction;
- the detected fringe period PDF and the detected fringe motion direction are transverse to the rotary measuring direction and depend at least partially on the nonzero yaw angle ψ;
- the high and low intensity bands move along the detected fringe motion direction transverse to the rotary measuring direction as the scale grating rotates about the rotary axis;
- 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 rotary measuring direction and provide respective spatial phase displacement signals that are indicative of the rotary scale displacement.