Optical encoder and measurement device including the same

Patent metadata

Field	Value
Publication number	US-10746573-B2
Application number	US-201816175053-A
Country	US
Kind code	B2
Filing date	Oct 30, 2018
Priority date	Nov 1, 2017
Publication date	Aug 18, 2020
Grant date	Aug 18, 2020

Abstract

An optical encoder includes a light source, a plurality of diffraction gratings including grating faces on which a plurality of grooves are disposed in parallel, and a light-receiving unit configured to receive the light diffracted at the plurality of diffraction gratings. The diffraction gratings include a first diffraction grating that is a first-stage diffraction grating adjacent to the light source, a third diffraction grating that is a last-stage diffraction grating adjacent to the light-receiving unit, and a second diffraction grating that is an output-stage diffraction grating of the first-stage diffraction grating and an input-stage diffraction grating of the last-stage diffraction grating. The diffraction gratings are disposed such that the ratio of the first gap to the third gap equals the ratio of the second gap to the fourth gap, and a length of the first gap differs from a length of the second gap.

First claim

The invention claimed is:

1. An optical encoder comprising:
a light source configured to emit parallel light;
a plurality of diffraction gratings including grating faces including a plurality of grooves disposed in parallel, the plurality of grooves being configured to diffract the parallel light; and
a light-receiving unit configured to receive light diffracted at the plurality of diffraction gratings,
wherein,
the optical encoder is configured to carry out measurement along a length measurement direction, where the length measurement direction is a direction of the plurality of grooves disposed in parallel and a direction orthogonal to the parallel light, and a depth direction is a direction orthogonal to the length measurement direction and the parallel light, and
a first axis extends in a direction orthogonal to the length measurement direction and the depth direction,
a second axis extends in a direction parallel to the first axis and is offset to the depth direction,
the plurality of diffraction gratings include:
a first-stage diffraction grating disposed at a first stage adjacent to the light source; and
a last-stage diffraction grating disposed at a last stage adjacent to the light-receiving unit, and
the first-stage diffraction grating and the last-stage diffraction grating are disposed such that
a ratio of a first gap to a third gap equals a ratio of a second gap to a fourth gap, and a length of the first gap differs from a length of the second gap, where the first gap is a gap along the first axis between the first-stage diffraction grating and an output-stage diffraction grating of the first-stage diffraction grating, the second gap is a gap along the second axis between the first-stage diffraction grating and the output-stage diffraction grating of the first-stage diffraction grating, the third gap is a gap along the first axis between the last-stage diffraction grating and an input-stage diffraction grating of the last-stage diffraction grating, and the fourth gap is a gap along the second axis between the last-stage diffraction grating and the input-stage diffraction grating of the last-stage diffraction grating.

2. The optical encoder according to claim 1 , wherein,
the plurality of diffraction gratings are formed in a planar shape, and
planes extending from grating faces of the plurality of diffraction gratings intersect each other on a straight line.

3. The optical encoder according claim 1 , wherein at least two of diffraction gratings of the plurality of diffraction gratings are formed in a stepwise shape and include a plurality of steps.

4. The optical encoder according to claim 1 , wherein the output-stage diffraction grating of the first-stage diffraction grating and the input-stage diffraction grating of the last-stage diffraction grating are the same diffraction grating.

5. The optical encoder according to claim 4 , wherein the first-stage diffraction grating and the last-stage diffraction grating are the same diffraction grating.

6. The optical encoder according to claim 1 , wherein the plurality of diffraction gratings are disposed such that the parallel light emitted from the light source is diffracted into a plurality of diffracted light beams at the first-stage diffraction grating, and the plurality of diffracted light beams intersect each other at the last-stage diffraction grating.

7. The optical encoder according to claim 1 , wherein, in a case that signal diffracted light is light traveling at predetermined diffraction angles on both sides of an optical axis of the light emitted from the light source, the first gap and the second gap satisfy:
| u 1− u 3|=2λ/sin 2 θ  (1)

where u 1 is the length of the first gap, u 3 is the length of the second gap, λ is a wavelength of the light source, and θ is an angle between a traveling direction of the signal diffracted light and a direction parallel to a direction of the optical axis of the light emitted from the light source.

8. A measurement device comprising:
the optical encoder according to claim 1 ;
a light source configured to emit parallel light;
a plurality of diffraction gratings including grating faces including a plurality of grooves disposed in parallel, the plurality of grooves being configured to diffract the parallel light; and
a light-receiving unit configured to receive the light diffracted at the plurality of diffraction gratings,
wherein the measurement device is configured to carry out measurement along a length measurement direction, where the length measurement direction is a direction of the plurality of grooves disposed in parallel and a direction orthogonal to the parallel light, and a depth direction is a direction orthogonal to the length measurement direction and the parallel light.

Assignees

• Mitutoyo Corp

Inventors

• Kimura Akihide

Classifications

• G01D5/38 Primary

  by diffraction gratings · CPC title

• G01D5/262 Primary

  with optical projection of a pointer or a scale · CPC title

• G01D5/34746

  Linear encoders · CPC title

• G02B27/60

  Systems using moiré fringes · CPC title

• G02B27/4277

  being separated by an air space · CPC title