Optical position-measuring device comprising two tracks each containing incremental graduations with integrated reference marks having aperiodic and periodic portions

Patent metadata

Field	Value
Publication number	US-10775202-B2
Application number	US-201916276636-A
Country	US
Kind code	B2
Filing date	Feb 15, 2019
Priority date	Feb 20, 2018
Publication date	Sep 15, 2020
Grant date	Sep 15, 2020

Abstract

An optical position-measuring device for determining the relative position of two objects includes two scanning units which are connected to one of the objects and each include a light source, one or more gratings and a detector assembly. A scale is connected to the other object and has two tracks each containing incremental graduations extending along a first one of the measurement directions. The incremental graduations each are composed of graduation regions which have different optical properties and are periodically arranged along an incremental graduation direction. The two incremental graduation directions form an angle of between 0° and 90° relative to each other. Each of the two incremental graduations has a reference mark integrated therein such that scanning of the reference mark allows a reference signal to be generated at a defined reference position along each of the measurement directions. The reference marks include both aperiodic and periodic portions.

First claim

What is claimed is:

1. An optical position-measuring device for determining the relative position of two objects that are movable relative to one another along at least two measurement directions, the optical position-measuring device comprising:
two scanning units which are connected to a first one of the two objects and each include at least one light source, one or more gratings and a detector assembly, and
a scale which is connected to a second one of the two objects and has two tracks each containing incremental graduations extending along a first one of the measurement directions, the incremental graduations each being composed of graduation regions which have different optical properties and are periodically arranged along an incremental graduation direction, the two incremental graduation directions forming an angle of between 0° and 90° relative to each other, and each of the two incremental graduations having at least one reference mark integrated therein such that scanning of the reference mark allows a reference signal to be generated at a defined reference position along each of the measurement directions, the reference marks including both aperiodic and periodic portions.

2. The optical position-measuring device as recited in claim 1 , wherein the reference marks are each disposed in a sub-area of limited extent in the respective incremental graduation, and wherein the aperiodic and periodic portions of the reference marks are intermixed within the sub-area.

3. The optical position-measuring device as recited in claim 2 , wherein the sub-area is rectangular in shape, and wherein a longitudinal axis of the rectangle is oriented perpendicular to the respective incremental graduation direction in the respective incremental graduation.

4. The optical position-measuring device as recited in claim 3 , wherein the rectangular reference mark extends across the entire width of the respective track containing the respective incremental graduation.

5. The optical position-measuring device as recited in claim 1 , wherein the aperiodic and periodic portions of the reference marks are configured spatially separately perpendicularly to the respective incremental graduation direction.

6. The optical position-measuring device as recited in claim 5 , wherein:
the periodic portion of the reference marks has a first reference mark grating constant that is identical to the respective incremental graduation grating constant; and
the aperiodic portion of the reference marks in each instance includes a plurality of grating structures having a second reference mark grating constant that varies spatially along the respective incremental graduation direction.

7. The optical position-measuring device as recited in claim 6 , wherein the aperiodic portion of the reference marks in each instance includes a plurality of mirror-symmetrically configured grating structures having the second reference mark grating constant which increases from a central axis of symmetry symmetrically outwardly perpendicularly to the respective incremental graduation direction.

8. The optical position-measuring device as recited in claim 5 , wherein the aperiodic portions of the reference marks are periodically arranged perpendicularly to the respective incremental graduation direction with a third reference mark grating constant.

9. The optical position-measuring device as recited in claim 8 , wherein the third reference mark grating constant is selected such that a displacement of one of the scanning units perpendicular to the incremental graduation direction will not produce a signal change.

10. The optical position-measuring device as recited in claim 5 , wherein the periodic and aperiodic portions of the reference marks have a surface area ratio of 1:1.

11. The optical position-measuring device as recited in claim 1 , wherein the periodic portion of the reference marks is integrated as a periodic superstructure into the aperiodic portion of the reference mark.

12. The optical position-measuring device as recited in claim 11 , wherein:
the periodic portion of the reference marks has a reference mark fine grating constant that is equal to the incremental graduation grating constant of the respective incremental graduation; and
the aperiodic portion of the reference marks is formed by two different reference mark regions which are alternately arranged along the respective incremental graduation direction with a reference mark coarse grating constant and which each have different ratios of graduation region width to the reference mark fine grating constant.

13. The optical position-measuring device as recited in claim 12 , wherein the differently configured reference mark regions are aperiodically arranged along the respective incremental graduation direction and, starting at a central axis of symmetry, the reference mark regions are arranged mirror-symmetrically and in each instance with outwardly increasing reference mark coarse grating constants.

14. The optical position-measuring device as recited in claim 1 , wherein:
a transmitting grating device is disposed in front of a divergently emitting light source in the scanning units, the transmitting grating device being composed of a periodic transmission-type transmitting grating and a transmitting slit adjacent thereto; and
the detector assembly includes an incremental signal detector and a reference signal detector.

15. The optical position-measuring device as recited in claim 1 , wherein the scale is in the form of a reflective scale and has alternately arranged reflective graduation regions having different phase-shifting effects.

Assignees

• Heidenhain Gmbh Dr Johannes

Inventors

• Hermann Michael

Classifications

• G01D2205/90

  Two-dimensional encoders, i.e. having one or two codes extending in two directions · CPC title

• G01D5/24438

  Special design of the sensing element or scale · CPC title

• G01D5/34746 Primary

  Linear encoders · CPC title

• G01D5/38

  by diffraction gratings · CPC title

• G01B11/00

  Measuring arrangements characterised by the use of optical techniques · CPC title