US-12618972-B2 - Optical position measuring device and method for operating an optical position measuring device

US12618972B2US 12618972 B2US12618972 B2US 12618972B2US-12618972-B2

Abstract

In an optical position measuring device for determining the position of two objects movable relative to each other along a measuring direction, a measuring standard includes a reflective measuring scale extending along the measuring direction and having scale regions with different reflectivities. A scanning unit arranged at a scanning distance relative to the measuring standard. Light source(s) and a detector arrangement including optoelectronic detector elements arranged periodically along the measuring direction are also provided. A signal processing unit is adapted to generate position signals relating to the relative position of the objects from the photocurrents generated by the detector elements, to determine a total photocurrent in a middle region and edge region(s) of the detector, and to determine the scanning distance from the photocurrent ratio of the total photocurrents formed in the middle region and edge region(s) of the detector.

Inventors

Daniel Frese
Jannik Jens Rosenlehner-Emde
Stefan Weis

Assignees

DR. JOHANNES HEIDENHAIN GMBH

Dates

Publication Date: 20260505
Application Date: 20221027
Priority Date: 20211029

Claims (19)

1 . An optical position measuring device for determining a position of a first object displaceable along a measuring direction relative to a second object, comprising: a measuring standard connected to the first object and including a reflective measuring scale extending along the measuring direction and having scale regions having different reflectivities, and a scanning unit connected to the second object and arranged at a scanning distance relative to the measuring standard, including at least one light source, and a detector arrangement including a plurality of optoelectronic detector elements located periodically along the measuring direction; and a signal processing unit associated with the scanning unit and adapted to generate, from photocurrents generated by the detector elements, position signals relating to the position of the first object relative to the second object, to determine a total photocurrent in a middle region of the detector and in at least one edge region of the detector, and to determine the scanning distance from a photocurrent ratio formed of total photocurrents in the middle region of the detector and in the edge region of the detector.
2 . The optical position measuring device according to claim 1 , wherein the signal processing unit is adapted to use values of the photocurrents used to generate position signals to form the photocurrent ratio.
3 . The optical position measuring device according to claim 1 , wherein the signal processing unit is adapted to determine a plurality of photocurrent ratios, to produce an average of the photocurrent ratios, and to determine the scanning distance from the averaged photocurrent ratio during a measuring operation.
4 . The optical position measuring device according to claim 1 , wherein the signal processing unit is adapted to determine the scanning distance from an analytical relationship.
5 . The optical position measuring device according to claim 1 , wherein the signal processing unit is adapted to determine the scanning distance from a table stored in the signal processing unit that describes a relationship between the determined photocurrent ratio and the scanning distance.
6 . The optical position measuring device according to claim 1 , wherein the measuring scale includes measuring scale element cells in which an area ratio of summed areas of a category of scale regions to a total area of element cells is constant, and the following relationship is satisfied: 0< V F =F TB1 /F GES <1, V F representing the area ratio, F TB1 representing the summed areas of the category of scale regions, and F GES representing the total element cell area.
7 . The optical position measuring device according to claim 6 , wherein the measuring scale is arranged as an incremental scale including a one-dimensional, alternating arrangement of rectangular or circular ring sector shaped scale regions having different reflectivities along the measuring direction.
8 . The optical position measuring device according to claim 6 , wherein the measuring scale includes a two-dimensional arrangement of scale regions having different reflectivities along the measuring direction and perpendicular to the measuring direction.
9 . The optical position measuring device according to claim 6 , wherein the measuring scale is arranged as pseudo random code including a one-dimensional, aperiodic arrangement of rectangular or circular ring sector shaped scale regions having different reflectivities along the measuring direction.
10 . The optical position measuring device according to claim 1 , wherein the detector arrangement includes a one-dimensional arrangement of rectangular or circular ring sector shaped detector elements located adjacent to each other along the measuring direction, longitudinal axes of the detector elements being oriented perpendicular to the measuring direction.
11 . The optical position measuring device according to claim 1 , wherein the detector arrangement includes a two-dimensional arrangement of detector elements located adjacent to each other along the measuring direction and perpendicular to the measuring direction.
12 . The optical position measuring device according to claim 1 , wherein the light source and the detector arrangement are arranged in a plane parallel to the measuring scale.
13 . A method for operating an optical position measuring device by which a position of a first object relative to a second object displaceable along a measuring direction is determined, the position measuring device including a measuring standard connected to the first object and having a reflective measuring scale extending along the measuring direction and including scale regions having different reflectivities, a scanning unit connected to the second object and arranged at a scanning distance relative to the measuring standard, the scanning unit including at least one light source and a detector arrangement including a plurality of optoelectronic detector elements located periodically along the measuring direction, and a signal processing unit associated with the scanning unit, comprising: generating, by the signal processing unit, position signals relating to the position of the first object relative to the second object from photocurrents generated by the detector elements; determining, by the signal processing unit, a total photocurrent in a middle region of the detector and in at least one edge region of the detector; and determining, by the signal processing unit, the scanning distance from a photocurrent ratio formed of total photocurrents in the middle region of the detector and in the edge region of the detector.
14 . The method according to claim 13 , wherein the signal processing unit uses values of the photocurrents used to generating the position signals to form the photocurrent ratio.
15 . The method according to claim 13 , wherein the signal processing unit determines a plurality of photocurrent ratios, produces an average of the photocurrent ratios, and determines the scanning distance from the averaged photocurrent ratio during a measuring operation.
16 . The method according to claim 13 , wherein the signal processing unit determines the scanning distance from an analytical relationship.
17 . The method according to claim 13 , wherein the signal processing unit determines the scanning distance from a table stored in the signal processing unit that describes a relationship between the determined photocurrent ratio and the scanning distance.
18 . The method according to claim 13 , wherein the signal processing unit uses twice as many detector elements in the middle region of the detector as in two edge regions of the detector symmetrical to the middle region of the detector to form the photocurrent ratio.
19 . An optical position measuring device for determining a position of a first object displaceable along a measuring direction relative to a second object, comprising: a measuring standard adapted to connect to the first object and including a reflective measuring scale extending along the measuring direction and having scale regions having different reflectivities, and a scanning unit adapted to connect to the second object and arranged at a scanning distance relative to the measuring standard, including at least one light source, and a detector arrangement including a plurality of optoelectronic detector elements located periodically along the measuring direction; and a signal processing unit associated with the scanning unit and adapted to generate, from photocurrents generated by the detector elements, position signals relating to the position of the first object relative to the second object, to determine a total photocurrent in a middle region of the detector and in at least one edge region of the detector, and to determine the scanning distance from a photocurrent ratio formed of total photocurrents in the middle region of the detector and in the edge region of the detector.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS The present application claims priority to Application No. 10 2021 212 224.8, filed in the German Patent and Trademark Office (Deutsche Patent- und Markenamt (DPMA)) on Oct. 29, 2021, which is expressly incorporated herein in its entirety by reference thereto. FIELD OF THE INVENTION The present invention relates to an optical position measuring device and to a method for operating an optical position measuring device, e.g., to determine the position of a first object relative to a second object. The position measuring device may include, for example, a reflective measuring scale connected to the first object and a scanning unit connected to the second object. The scanning distance between the measuring scale and the scanning unit may be determined by a signal processing unit. BACKGROUND INFORMATION Particularly for optical position measuring devices that work with incident light and include a measuring device having a reflective measuring scale, it is of interest to capture the scanning distance between the measuring scale and the scanning unit in addition to the actual position information. For modularly constructed position measuring devices, this information can be used during installation in the particular application, for example, in order to correctly set the scanning distance. During measuring operation, it is possible, for example, for a corresponding, rotational variant of such a position measuring device, to draw conclusions from the continuous monitoring of the scanning distance about shifting of the rotating shaft or with respect to thermal influences. A series of approaches are conventional for determining the scanning distance in such position measuring devices. Japanese Patent Document No. 2001-174287 describes that the light emitted by an additional light source for measuring the scanning distance is guided onto a reflector track disposed between two measuring scale tracks on a measurement scale. The reflected light impinges on a detector in the scanning unit, in which the beam diameter of the of the beam bundle impinging on the detector changes as a function of the scanning distance. The scanning distance can be estimated by an intensity measurement. With this approach, in addition to the components for measuring position, a further light source, a separate reflector track, and an additional detector are required accordingly in order to obtain the information relating to the scanning distance. The approaches described in Japanese Patent Document Nos. 2013-113634 and 2016-050886 do not require such additional components. In this regard, the grating structure of the measuring scale is illuminated for measuring each position, and the grating self-images being formed periodically along the scanning distance direction are evaluated according to the Talbot effect. The amplitudes of the grating self-images represent the measurement of the scanning distance of interest. A disadvantage is that periodic grating structures on the measuring scale are necessary, that is, determining the scanning distance is not possible in conjunction with an aperiodic code structure. Light sources meeting particular coherence requirements are also required for these measurement methods. A further approach is described in German Patent Document No. 10 2018 104 280, which describes using the detector both for position measurement and for determining changes in the scanning distance in reflective position measuring devices. As a measure of the change of the scanning distance, the changes in intensity and/or the location of the light reflected back from the measuring scale, as captured by the detector, are evaluated. Changes in the scanning distance can be determined at a resolution of about 0.1 mm. For monitoring the corresponding position measuring device, particularly during measuring operation, however, such a resolution for determining the scanning distance is too low. Furthermore, evaluating the light intensity for determining the distance cannot be combined well with typical methods for stabilizing the illumination of the measuring scale in a manner that is acceptable for operating the position measuring device. SUMMARY Example embodiments of the present invention provide an optical position measuring device and a method for operating an optical position measuring device, in which the scanning distance can be determined as precisely as possible without additional components being necessary. According to an example embodiment of the present invention, an optical position measuring device is configured to determine the position of a first object displaceable relative to a second object along a measuring direction. A measuring standard having a reflective measuring scale extending along the measuring direction and including scale regions having different reflectivities is connected to the first object. A scanning unit is connected to the second object and is disposed at a scannin