CN112880571A - Absolute grating ruler - Google Patents

Absolute grating ruler Download PDF

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CN112880571A
CN112880571A CN202110290002.9A CN202110290002A CN112880571A CN 112880571 A CN112880571 A CN 112880571A CN 202110290002 A CN202110290002 A CN 202110290002A CN 112880571 A CN112880571 A CN 112880571A
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coding
scale
value
code
absolute grating
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于海
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Changchun Institute of Optics Fine Mechanics and Physics of CAS
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B11/00—Measuring arrangements characterised by the use of optical techniques
    • G01B11/02—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness

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Abstract

The invention belongs to the technical field of photoelectric displacement precision measurement, and relates to an absolute grating ruler which comprises a scale, a sliding guide rail and a reading head, wherein the sliding guide rail is arranged above a ruler body of the scale, is parallel to the extending direction of the ruler body and is vertical to a coding marking surface of the ruler body, and the reading head is arranged on the sliding guide rail and can linearly move along the sliding guide rail. A group of coding values are formed by numerical values represented by any N adjacent coding marked lines in the M coding marked lines, a decoding value C of the corresponding coding value is obtained, a subdivision value S is obtained by utilizing an image collected by the reading head, and the subdivision value S is combined with the decoding value C to obtain a linear displacement measurement numerical value. The invention adopts the linear array image sensor to realize the identification and subdivision of the displacement, and can realize higher resolution and measurement precision than the traditional technology; the full-digital operation image recognition system is adopted, so that the anti-jamming capability is stronger and the service life is longer.

Description

Absolute grating ruler
Technical Field
The invention belongs to the technical field of photoelectric displacement precision measurement, and particularly relates to an image type high-resolution absolute grating ruler.
Background
Along with the development of novel industrial equipment such as major axis digit control machine tool, traditional incremental displacement measurement equipment has been unable to satisfy the demand of manufacture equipment. Because the absolute linear displacement measurement has the characteristic of directly obtaining the position information when the numerical control system is powered on for the first time, the numerical control system can immediately enter a working state or continue to operate last time without return-to-zero operation, and the working efficiency of the equipment is greatly improved.
The research of the absolute grating ruler in China starts late, the research of the single-track position absolute coding is broken through in 2009 by the Changchun optical engine, and the absolute decoding and subdivision are realized by a mixed code channel method in cooperation with the incremental code channel. On the basis of the research, scholars such as Changchun bare engine institute, Jilin university, Changchun science and engineering university, Guangdong industrial university, combined fertilizer industry university and the like develop key technical research on the absolute grating ruler, and the adopted scheme mostly follows the method proposed by the Changchun bare engine institute 2009; and the measurement resolution of 0.01 mu m is realized at most, and the subdivision method still depends on the moire fringe technology.
The existing absolute grating ruler can realize absolute measurement only by matching a plurality of code channels, and needs to perform steps of aligning phases, periodically correcting signals of the plurality of code channels in installation and debugging, and the debugging process is complicated. Meanwhile, most of the domestic absolute grating scales still adopt the moire fringe technology to realize subdivision operation, are influenced by factors such as process level, signal noise, installation precision and the like, and the performance realized by adopting the moire fringe technology reaches the bottleneck.
With the development of digital image processing technology, the adoption of the image processing technology can surpass the traditional technology to realize measurement with higher resolution; because the acquired image is composed of a plurality of pixel information, absolute decoding and subdivision can be realized by adopting a single code channel, and the method is more favorable for researching a displacement measurement technology with high resolution.
Disclosure of Invention
In order to overcome the defects of the prior art, the linear array image sensor is adopted to realize the identification and subdivision of the displacement, and higher resolution and measurement precision can be realized compared with the traditional technology. And the image recognition system adopts full digital operation, so that the anti-interference capability is stronger and the service life is longer. In order to achieve the purpose, the invention adopts the following specific technical scheme:
an absolute grating scale comprising: the scale, the sliding guide rail and the reading head arranged on the sliding guide rail;
the sliding guide rail is parallel to the extending direction of the scale body of the scale and is vertical to the coding marking surface of the scale body(ii) a The numerical values represented by any N adjacent coding marked lines in the M coding marked lines on the ruler form a group containing N coding elements Xi，Xi+1，…，Xi+N-2，Xi+N-1Obtaining a coded value C of the corresponding coded value, wherein i is 1, 2, …, M;
and (3) calculating and acquiring a subdivision value S by using an image acquired by a reading head through an equation (1):
Figure BDA0002982023130000021
in the formula, Z1And Z2Respectively the centroid positions of two adjacent coding marked lines;
Zcrepresenting a center point of the image;
K＝2Mrepresents the subdivision factor;
and combining the subdivision value S with the decoding value C to obtain a linear displacement measurement value Data.
Preferably, the M coding marked lines on the ruler body are positioned on the same transverse shaft, the coding marked lines are transparent rectangular marked lines, and the distances between the centers of mass are the same.
Preferably, the coding markings comprise a wide coding marking and a narrow coding marking; the wide code scale line represents code element "1", and the narrow code scale line represents code element "0".
Preferably, the width D of the wide code reticle1Not more than L/M; width D of narrow coded reticle2Not more than L/2M; l is the measurement length.
Preferably, N is the number of binary bits of the number M of coded markings, M being 2NAnd N is a preset value.
Preferably, the ith symbol XiCalculated from the following formula:
Figure BDA0002982023130000022
in the formula (I), the compound is shown in the specification,
Figure BDA0002982023130000023
representing an exclusive or operation;
a1～aNthe coefficients are respectively calculated to have values of "1" or "0", and are not all "0".
Preferably, the measurement Data is calculated by:
Data＝C×K+S (3)。
preferably, the reading head comprises: the linear array image sensor, the data processing circuit, the light emitting module and the sliding support;
the linear array image sensor and the light-emitting module are respectively positioned at the upper side and the lower side of the scale through the support of the sliding support and are close to the scale, so that the image receiving of the coding mark line is realized;
the pixel arrangement direction of the linear array image sensor is parallel to the arrangement direction of the coding marked lines;
the light emitting module is used for providing light rays penetrating through the coding marked line;
the data processing circuit is used for receiving the image data of the linear array image sensor, and performing subdivision operation according to the image data to realize decoding operation.
Preferably, the light emitting module can cover parallel light sources of N adjacent code marked lines, and the diameter of a light spot emitted by the light emitting module is not less than N.L/M.
Preferably, the device also comprises an output cable which is connected with the reading head and outputs the measurement Data obtained by calculation processing.
The invention can obtain the following technical effects:
1. the linear array image sensor is adopted to realize the identification and subdivision of the displacement, and higher resolution and measurement precision can be realized compared with the traditional technology.
2. The full-digital operation image recognition system is adopted, so that the anti-jamming capability is stronger and the service life is longer.
Drawings
FIG. 1 is a schematic diagram of an absolute grating scale according to an embodiment of the present invention;
FIG. 2 is a schematic view of a section of a grating scale encoder reticle of one embodiment of the present invention;
FIG. 3 is a schematic view of a readhead according to one embodiment of this invention;
FIG. 4 is a schematic illustration of the subdivision principle of one embodiment of the present invention;
fig. 5 is a schematic diagram of another image-based high-resolution absolute grating scale according to an embodiment of the present invention.
Reference numerals:
scale 1, scale body 11, code marking 12, wide code marking 121, narrow code marking 122,
A reading head 2, a linear array image sensor 21, a data processing circuit 22, a light-emitting module 23, a sliding support 24,
Output cable 3, sliding guide 4.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not to be construed as limiting the invention.
The invention aims to provide an image type high-resolution absolute grating scale, which can simply and conveniently realize image recognition of a coding marking on the scale, and further realize high-resolution and high-precision linear displacement measurement. The absolute grating ruler provided by the invention will be described in detail through specific embodiments.
As shown in fig. 1, comprises a scale 1, a reading head 2 and a sliding guide rail 4; the sliding guide rail 4 is positioned on the scale 1, is parallel to the extending direction of the scale body 11 and is vertical to the surface of the scale body 11 with the coded marked lines 12; the reading head 2 is mounted on the slide rail 4 and can linearly move along the slide rail 4.
A group of numerical values containing N coding elements X is formed by numerical values represented by any N adjacent coding marked lines 12 in M coding marked lines 12 on the ruler body 11i，Xi+1，…，Xi+N-2，Xi+N-1(i-1, 2, …, M), and obtaining a decoding value C of the corresponding encoding value by looking up a table;
and then, obtaining a subdivision value S through calculation by utilizing an image acquired by the reading head 2, and combining the subdivision value S with the decoding value C to obtain a linear displacement measurement value Data of the grating ruler.
In another embodiment of the invention, the readhead 2 is used to achieve a searchlight on the scale 1, and the readhead 2 will always maintain a searchlight on the scale 1 as the readhead 2 moves along the sliding guide 4.
In a preferred embodiment of the present invention, as shown in FIG. 2, the scale body 11 of the scale 1 has M code marks 12 on the same horizontal axis, in terms of X1～XMThe coding marked lines 12 are all transparent rectangular marked lines, and the distances between the centers of mass are the same. And if the measurement length of the absolute grating ruler is L, the distance between the centroids of the adjacent code marked lines 12 is L/M.
With continued reference to fig. 2, the code reticle 12 contains a wide code reticle 121 representing a code element of "1" and a narrow code reticle 122 representing a code element of "0". Wherein, the width D of the wide code marking 1211Not more than L/M; width D of narrow code reticle 1222Not more than L/2M.
The values represented by the wide code markings 121 and the narrow code markings 122 form a group of N-bit shift cyclic codes, where N is the number of binary bits of the number M of code markings 12, and N is a preset value.
In a preferred embodiment of the invention, the coding element X is setiFor the value represented by the i-th code mark 12 (i ═ 1, 2, …, M), the N code marks 12 that are successively adjacent will form a group of code values, denoted by { X {i，Xi+1，…，Xi+N-2，Xi+N-1H, then the ith value X in the set of encoded valuesiCan be calculated by the formula (2):
Figure BDA0002982023130000051
in the formula (I), the compound is shown in the specification,
Figure BDA0002982023130000052
representing an exclusive or operation;
a1～aNare respectively an arithmetic coefficient, the value of which is "1 "is alternatively" 0 "and not all" 0 ".
Calculate each bit X in turniAnd the coefficient a is appropriately selected1～aNCan be calculated to a value of at most 2NAn encoded value. The corresponding value of i is the decoded value C.
In another embodiment of the invention, given different values of N, the corresponding coefficient values are: that is, when N is 7, a1～a7＝{1，0，1，0，1，1，1}；
When N is 8, a1～a8＝{1，0，0，0，1，1，1，0，1}；
When N is 9, a1～a9＝{1，0，0，0，0，1，0，0，0，1}；
When N is 10, a1～a10＝{1，0，0，0，0，0，0，1，0，0，1}。
In a preferred embodiment of the present invention, as shown in fig. 3, the reading head 2 comprises a line image sensor 21, a data processing circuit 22, a light emitting module 23 and a sliding support 24.
The linear array image sensor 21 and the light-emitting module 23 are respectively positioned at the upper side and the lower side of the scale 1 through the support of the sliding support 24;
the linear array image sensor 21 is close to the scale 1, does not influence sliding, and realizes image receiving of the coding marked line 12; the pixel arrangement direction of the linear array image sensor 21 is parallel to the arrangement direction of the coding marked lines 12;
the light emitting module 23 is used for providing light rays penetrating the code marked line 12;
the data processing circuit 22 receives image data of the line image sensor 21, performs a subdivision operation on the image data, and performs a decoding operation.
In another embodiment of the present invention, the preset threshold Th ═ D (D)1+D2) The data processing circuit 22 performs binarization on the received image data, and determines that the symbol is "1" when the width of the collected code mark line 12 is larger than Th value and "0" when the width is smaller. N adjacent code elements X in each image acquisitioni，Xi+1，…，Xi+N-2，Xi+N-1Combining into a set of encoded values, and then looking up the corresponding decoding table (see table 1), the corresponding decoding value C, denoted as C ═ i, can be obtained.
Fig. 4 illustrates the subdivision principle of an embodiment of the invention, see fig. 4:
setting the position of the central line of the image as ZcThen the pixel values of the two code reticle 12 on either side of the position C adjacent thereto are retained according to the algorithm. Respectively calculating the centroid positions of the two coding marked lines 12 by adopting a centroid algorithm, and respectively recording the centroid positions as Z1And Z2Then, the subdivision operation can be expressed as equation (1):
Figure BDA0002982023130000061
combining the subdivision value S in equation (1) with the decoding value C, the linear displacement measurement value of the absolute grating scale can be obtained as follows:
Data＝C×K+S (3)。
in a preferred embodiment of the present invention, the present invention further comprises an output cable 3 interconnected with the reading head 2 for outputting the calculated linear displacement measurement Data.
Fig. 5 shows a schematic structural diagram of another embodiment of the present invention, which includes: scale 1, reading head 2, output cable 3 and sliding guide 4.
In the reading head 2, the line image sensor 21 and the light emitting module 23 are located on the same side of the scale 1. The scale body 11 of the scale 1 is made of reflective materials, and the code marked lines 12 are made of non-reflective materials. The parallel light emitted by the light emitting module 23 is reflected by the ruler body 11, and then the pattern of the coding marked line 12 is reflected to the linear array image sensor 21, so that emission imaging is realized. And the current linear displacement information is obtained through the acquisition of the linear array image sensor 21 and the operation of the processing circuit 22.
Table 1 coding table N-7
Figure BDA0002982023130000062
Figure BDA0002982023130000071
In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, various embodiments or examples and features of different embodiments or examples described in this specification can be combined and combined by one skilled in the art without contradiction.
Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention, and that variations, modifications, substitutions and alterations can be made to the above embodiments by those of ordinary skill in the art within the scope of the present invention.
The above embodiments of the present invention should not be construed as limiting the scope of the present invention. Any other corresponding changes and modifications made according to the technical idea of the present invention should be included in the protection scope of the claims of the present invention.

Claims (10)

1. An absolute grating scale, comprising: the scale, the sliding guide rail and the reading head arranged on the sliding guide rail;
the sliding guide rail is parallel to the extending direction of the scale body of the scale and is vertical to the coding marking surface of the scale body; forming a group of N coding elements by numerical values represented by any N adjacent coding marked lines in M coding marked lines on the ruler bodyXi，Xi+1，…，Xi+N-2，Xi+N-1Obtaining a coded value C corresponding to said coded value, wherein i is 1, 2, …, M;
and calculating and acquiring a subdivision value S by using an image acquired by the reading head through an equation (1):
Figure FDA0002982023120000011
in the formula, Z1And Z2Respectively the centroid positions of two adjacent coding marked lines;
Zcrepresenting a center point of the image;
K＝2Mrepresents the subdivision factor;
and combining the subdivision value S with the decoding value C to obtain a linear displacement measurement value Data.
2. The absolute grating ruler of claim 1, wherein the M coding marks on the ruler body are located on the same transverse axis, and the coding marks are transparent rectangular marks with the same center-of-mass distance.
3. The absolute grating scale of claim 2, wherein the code reticle comprises a wide code reticle and a narrow code reticle; the wide code reticle represents a code element "1" and the narrow code reticle represents a code element "0".
4. The absolute grating scale of claim 3, wherein the width D of the wide code reticle1Not more than L/M; width D of the narrow coding reticle2Not more than L/2M; l is the measurement length.
5. The absolute grating ruler of claim 4, wherein N is the number of binary bits of the number M of code reticles, and N is a preset value.
6. The absolute grating scale of claim 5, wherein the ith code element XiCalculated from the following formula:
Figure FDA0002982023120000012
in the formula (I), the compound is shown in the specification,
Figure FDA0002982023120000013
representing an exclusive or operation;
a1～aNthe values of the arithmetic coefficients are "1" or "0", and are not all "0".
7. The absolute grating ruler of claim 6, wherein the measurement Data is calculated by the following formula:
Data＝C×K+S(3)。
8. the absolute grating scale of claim 1, wherein the reading head comprises: the linear array image sensor, the data processing circuit, the light emitting module and the sliding support;
the linear array image sensor and the light-emitting module are respectively positioned at the upper side and the lower side of the scale through the support of the sliding support and are close to the scale, so that the image receiving of the coding marked line is realized;
the pixel arrangement direction of the linear array image sensor is parallel to the arrangement direction of the coding marked lines;
the light emitting module is used for providing light rays penetrating through the coding marked line;
the data processing circuit is used for receiving the image data of the linear array image sensor, and performing subdivision operation according to the image data to realize decoding operation.
9. The absolute grating ruler of claim 8, wherein the light emitting module can cover the parallel light sources of the N adjacent code reticle lines, and the diameter of the light spot emitted by the light emitting module is not less than N · L/M.
10. The absolute grating ruler of claim 1, further comprising an output cable connected to the reading head for outputting the calculated measurement Data.
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CN116858134A (en) * 2023-07-07 2023-10-10 北京控制工程研究所 High-precision photoelectric angular displacement sensor position resolving method and device
CN118583064A (en) * 2024-08-05 2024-09-03 中国科学院长春光学精密机械与物理研究所 Displacement measurement method and system capable of compensating measurement interval change error of reading head

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