Optical position-measuring device

Patent metadata

Field	Value
Publication number	US-11313672-B2
Application number	US-202016869606-A
Country	US
Kind code	B2
Filing date	May 8, 2020
Priority date	May 14, 2019
Publication date	Apr 26, 2022
Grant date	Apr 26, 2022

Abstract

An optical position-measuring device for sensing a relative position of two objects, each object being connected to a grating. The optical position-measuring device is configured such that, at one of the gratings, an illumination beam emitted from a light source is split into two sub-beams which, in respective scanning beam paths following the splitting, experience different polarization-optical effects and recombine at one of the gratings. After the differently polarized sub-beams are recombined, a plurality of phase-shifted, displacement-dependent scanning signals are generatable from a resulting signal beam in a detection unit. No separate polarization-optical components are disposed in the scanning beam paths of the sub-beams between splitting and recombination. At least one of the gratings is configured as a polarization grating configured to produce the different polarization-optical effects and such that diffraction orders with different polarization states are produced at each point of incidence on the polarization grating.

First claim

What is claimed is:

1. An optical position-measuring device for sensing a relative position of two objects which are movable relative to one another along at least one measurement direction, the optical position-measuring device comprising:
a first grating configured to be connected to the first object and a second grating configured to be connected to the second object,
wherein the optical position-measuring device is configured such that, at one of the gratings, an illumination beam emitted from a light source is split into at least two sub-beams which, in respective scanning beam paths following the splitting, experience different polarization-optical effects and recombine at one of the gratings, wherein after the differently polarized sub-beams are recombined, a plurality of phase-shifted, displacement-dependent scanning signals are generatable from a resulting signal beam,
wherein no separate polarization-optical components are disposed in the scanning beam paths of the at least two sub-beams between splitting and recombination,
wherein at least one of the gratings is configured as a polarization grating configured to produce the different polarization-optical effects on the at least two sub-beams, and
wherein the polarization grating is configured such that diffraction orders with different polarization states are produced independent of location on the polarization grating.

2. The optical position-measuring device as recited in claim 1 , wherein an area fill ratio FV of the polarization grating is selected according to the relation FV<0.6, where the area fill ratio FV is defined as a ratio of an area of the grating lines within a polarization grating unit cell to an overall area of the polarization grating unit cell.

3. The optical position-measuring device as recited in claim 1 , wherein the polarization grating is configured such that resulting +/− 1 st diffraction orders are polarized orthogonally to each other.

4. The optical position-measuring device as recited in claim 1 , wherein:
the first object is connected to the first grating which is configured as a reflection phase grating or as a transmission phase grating,
the second object is connected to the second grating which is configured to function as the polarization grating and is configured as a reflection phase grating,
the illumination beam emitted from the light source is split at the first grating into the at least two sub-beams which subsequently strike the second grating, where each of the at least two sub-beams experiences diffraction and a change in direction, the at least two sub-beams being polarized orthogonally to each other after striking the second grating, and
the at least two sub-beams impinge on the first grating again, where the at least two sub-beams are recombined, so that a resulting signal beam then propagates toward a detector.

5. The optical position-measuring device as recited in claim 1 , wherein:
the first object is connected to the first grating which functions as a scale and is configured as a reflection phase grating or as a transmission phase grating,
the second object is connected to a scanning unit, the scanning unit including the following components:
the light source,
the second grating which is configured to function as a scanning grating and as the polarization grating and which is configured as a reflection phase grating, and
a detector,

wherein:
the illumination beam emitted from the light source is split at the first grating into the at least two sub-beams,
the at least two sub-beams subsequently strike the second grating, where each of the at least two sub-beams experiences a change in direction, the at least two sub-beams being polarized orthogonally to each other after striking the second grating, and
the at least two sub-beams impinge on the first grating again, where the at least two sub-beams are recombined, so that a resulting signal beam then propagates toward the detector.

6. The optical position-measuring device as recited in claim 1 , wherein the polarization grating includes a plurality of arcuately curved grating structures in the form of grating lines and grating spaces, a direction of longitudinal extent of each of these grating structures being oriented parallel to the measurement direction, and the grating structures being arranged periodically both along the measurement direction and perpendicularly to the measurement direction.

7. The optical position-measuring device as recited in claim 6 , wherein the polarization grating has strip-shaped grating sections periodically arranged parallel to the measurement direction with a periodicity in the measurement direction, a direction of longitudinal extent of the grating sections being oriented perpendicularly to the measurement direction, the grating structures within the grating sections being periodically arranged perpendicularly to the measurement direction with an orthogonal periodicity Λ_ortho.

8. The optical position-measuring device as recited in claim 6 , wherein between adjacent grating sections of the polarization grating, there is disposed at least one of:
a grating space,
a grating line, or
a plurality of alternating adjacent grating lines and grating spaces.

9. The optical position-measuring device as recited in claim 6 , wherein grating structures of adjacent grating sections adjoin one another.

10. The optical position-measuring device as recited in claim 7 , wherein the orthogonal periodicity Λ_ortho is selected according to the relation Λ_ortho <1.5·λ, where λ is the wavelength of the light source used.

11. The optical position-measuring device as recited in claim 1 , wherein the polarization grating is configured as a reflection phase grating having grating lines and grating spaces with different reflective properties.

12. The optical position-measuring device as recited in claim 11 , wherein the reflection phase grating includes:
a carrier substrate,
a planar reflective layer disposed on the carrier substrate, and
a grating structure layer disposed above the reflective layer.

13. The optical position-measuring device as recited in claim 12 , wherein the grating structure layer has a layer thickness d selected according to the relation d <0.6·λ, where λ is the wavelength of the light source used.

14. The optical position-measuring device as recited in claim 12 , wherein a planar phase-shifting layer is disposed between the planar reflective layer and the grating structure layer.

15. The optical position-measuring device as recited in claim 12 , wherein:
the reflective layer is composed of a metallic reflective layer or of a reflective layer stack, and
the grating structure layer is composed of a dielectric material selected from the group consisting of SiO 2 , TaO x , TiO 2 and Si, or of a semiconductor material selected from the group consisting of TiN and GaN, or of a layer stack including one or more of the dielectric materials and one or more of the semiconductor materials.

16. An optical position-measuring device for sensing a relative position of two objects which are movable relative to one another along at least one measurement direction, the optical position-measuring device comprising:
a first grating configured to be connected to the first object and a second grating configured to be connected to the second object,
wherein the optical position-measuring device is configured such that, at one of the gratings, an illumination beam emitted from a light source is split into at least two sub-beams which, in respective scanning beam paths following the splitting, experienc

Assignees

• Heidenhain Gmbh Dr Johannes

Inventors

• Kaelberer Thomas

Classifications

• G01B11/02

  for measuring length, width or thickness (G01B11/08 takes precedence) · CPC title

• G01D5/344 Primary

  using polarisation (G01D5/35303 takes precedence) · CPC title

• G02B27/10

  Beam splitting or combining systems (polarising systems G02B27/28; mixing and splitting light signals using optical waveguides G02B6/28; {beam shaping, e.g. changing the cross-sectional area, by dividing or superposing multiple light beams G02B27/0905}) · CPC title

• G01D5/38

  by diffraction gratings · CPC title

• G02B27/283

  used for beam splitting or combining · CPC title