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

Patent metadata

Field	Value
Publication number	US-10295378-B2
Application number	US-201715702520-A
Country	US
Kind code	B2
Filing date	Sep 12, 2017
Priority date	Jun 29, 2017
Publication date	May 21, 2019
Grant date	May 21, 2019

Abstract

An optical encoder configuration comprises a scale, an illumination source, and a photodetector configuration. The illumination source is configured to output structured illumination to the scale. The scale extends along a measuring axis direction and is configured to output scale light that forms a detector 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 along a detected fringe motion direction transverse to the measuring axis direction. 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. The photodetector configuration is configured to detect a displacement of the high and low intensity bands along the detected fringe motion direction and provide respective spatial phase displacement signals that are indicative of the scale displacement.

First claim

What is claimed is:

1. 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 P SF 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.

2. The contamination and defect resistant optical encoder configuration of claim 1 , wherein the structured illumination generating portion comprises a first illumination source light diffraction grating and a second illumination source light diffraction grating.

3. The contamination and defect resistant optical encoder configuration of claim 2 , wherein the first illumination source light diffraction grating and the second illumination source light diffraction grating are phase gratings.

4. The contamination and defect resistant optical encoder configuration of claim 1 , wherein N is an integer that is at least 6.

5. The contamination and defect resistant optical encoder configuration of claim 4 , wherein:
the spatial phase detectors are arranged in the spatial phase sequence along the detected fringe motion direction, where N is an integer that is at least 6 and the spatial phase sequence comprises two outer spatial phase detectors at a start and end of the spatial phase sequence along the detected fringe motion direction transverse to the measuring axis direction and an interior group of spatial phase detectors located between the two outer spatial phase detectors;
each spatial phase detector in the interior group is preceded and followed in the spatial phase sequence by spatial phase detectors that have respective spatial phases that are different from that spatial phase detector and different from each other; and
each spatial phase detector comprises scale light receptor areas that are spatially periodic along the detected fringe motion direction and positioned corresponding to a respective spatial phase of that spatial phase detector relative to a periodic scale light pattern.

6. The contamination and defect resistant optical encoder configuration of claim 5 , wherein the set of N spatial phase detectors comprises at least M subsets of spatial phase detectors, where M is an integer that is at least 2, and wherein each of the M subsets includes spatial phase detectors that provide each of the respective spatial phases included in the set of N spatial phase detectors.

7. The contamination and defect resistant optical encoder configuration of claim 6 , wherein M is at least 4.

8. The contamination and defect resistant optical encoder configuration of claim 6 , wherein M is at least 6.

9. The contamination and defect resistant optical encoder configuration of claim 6 , wherein each of the M subsets of spatial phase detectors comprises spatial phase detectors that provide the same respective spatial phases arranged in the same subset spatial phase sequence.

10. The contamination and defect resistant optical encoder configuration of claim 9 , wherein each subset of spatial phase detectors comprises 3 spatial phase detectors having respective spatial phases separated by 120 degrees.

11. The contamination and defect resistant optical encoder configuration of claim 9 , wherein N is at least 8 and each subset of spatial phase detectors comprises 4 spatial phase detectors having respective spatial phases separated by 90 degrees.

12. The contamination and defect resistant optical encoder configuration of claim 5 , wherein the photodetector configuration includes connections configured to combine spatial phase detector signals corresponding to the same respective spatial phase and to output each such combination as a respective spatial phase position signal.

13. The contamination and defect resistant optical encoder configuration of claim 12 , wherein the photodetector configuration is configured to output 3 spatial phase position signals corresponding to spatial phases separated by 120 degrees.

14. The contamination and defect resistant optical encoder configuration of claim 12 , wherein the photodetector configuration is configured to output 4 spatial phase position signals corresponding to spatial phases separated by 90 degrees.

15. The contamination and defect resistant optical encoder configuration of claim 5 , wherein a separation distance YSEP between the scale light receptor areas of each adjacent pair of the N spatial phase detectors along the detected fringe motion direction is at most 25 micrometers.

16. The contamination and defect resistant optical encoder configuration of claim 5 , wherein a separation distance YSEP between the scale light receptor areas of each adjacent pair of the N spatial phase detectors is the same along the detected fringe motion direction.

17. The contamination and defect resistant optical encoder configuration of claim 5 , wherein each of the N spatial phase detectors comprises

Assignees

• Mitutoyo Corp

Inventors

• Tobiason Joseph Daniel
• Laman Norman
• Kimura Akihide
• Hirata Shu

Classifications

• G01D5/24428

  Error prevention · CPC title

• G01D5/34715 Primary

  Scale reading or illumination devices · CPC title

• G01D5/24438 Primary

  Special design of the sensing element or scale · CPC title

• G01D5/38

  by diffraction gratings · CPC title

• G01D5/30

  the beams of light being detected by photocells · CPC title