CN112361995A

CN112361995A - Visual absolute type rotation angle measuring method and device

Info

Publication number: CN112361995A
Application number: CN202011391712.2A
Authority: CN
Inventors: 王德麾; 姜世平; 杨武; 代冬军; 郑鑫; 力昌兵
Original assignee: Sichuan Windom Photoelectric Technology Co ltd
Current assignee: Sichuan Windom Photoelectric Technology Co ltd
Priority date: 2020-12-02
Filing date: 2020-12-02
Publication date: 2021-02-12
Anticipated expiration: 2040-12-02
Also published as: CN112361995B

Abstract

The invention provides a vision absolute type rotation angle measuring method and device, wherein the device comprises a CCD camera and an annular code wheel, and the middle part of the code wheel rotates through a connecting rotating shaft; n co-circular gray scale marks are uniformly distributed on the ring of the code disc, and the gray scale value of each gray scale mark corresponds to n-level gray scale values which are set at uniform intervals in a 0-255 gray scale value interval respectively; the CCD camera is arranged above the code disc, so that the shooting visual field of the CCD camera is aligned to the gray scale mark, and at least one complete gray scale mark exists in the shooting visual field at any moment. The measuring device has absolute positioning capability and extremely small rotation angle measuring resolution.

Description

Visual absolute type rotation angle measuring method and device

Technical Field

The invention relates to the technical field of angle measurement, in particular to a visual absolute type rotation angle measuring method and device.

Background

The precision measurement of the plane moving distance is a common general requirement, is often applied to a closed-loop servo system of a numerical control machine tool, and can be used for detecting the linear displacement or the angular displacement. At present, the industrial field mainly adopts grating ruler measurement, which is also called as a grating ruler displacement sensor or a grating ruler sensor, and the grating ruler displacement sensor or the grating ruler sensor is a measurement feedback device which works by utilizing the optical principle of a grating.

The materials for manufacturing the grating mainly comprise the following 2 materials:

1. reticle glass ruler (effective measuring length used below 3 meters)

2. Reticle steel belt ruler (effective measuring length for more than 3 meters)

Under special working conditions with vibration, impact and high reliability requirements, non-vitreous materials can be used as far as possible. However, the precise metal grating has complex manufacturing process and higher cost. Besides, it has several problems:

1. the grating ruler can only perform incremental measurement of position offset compared with the previous position, namely, after the system is powered on for the first time, the current position cannot be obtained, zero position searching needs to be performed firstly, and then the current position can be obtained by accumulating historical movement data. After the system is powered off and the fault is restarted at any time, the above processes are repeated to obtain the current position information.

2. Measurement errors continue to accumulate. That is, once a positioning error occurs at a certain position, the error is always present and cannot be eliminated, and the positioning error cannot be recovered unless the positioning error passes through the zero position again.

3. In principle, the traditional absolute grating encoder is difficult to achieve high resolution. And the structure is more complicated and the cost is higher.

Disclosure of Invention

The invention aims to provide a visual absolute type rotation angle measuring method and device to solve the problems in the measurement by using a grating ruler.

The invention provides a visual absolute type rotating angle measuring device which comprises a CCD camera and an annular coded disc, wherein the middle part of the coded disc rotates through a connecting rotating shaft;

n co-circular gray scale marks are uniformly distributed on the ring of the code disc, and the gray scale value of each gray scale mark corresponds to n-level gray scale values which are set at uniform intervals in a 0-255 gray scale value interval respectively;

the CCD camera is arranged above the code disc, so that the shooting visual field of the CCD camera is aligned to the gray scale mark, and at least one complete gray scale mark exists in the shooting visual field at any moment.

Further, the gray values of the adjacent gray marks are different by at least 2 gray values.

Further, the gray marks are solid circles.

Further, n is 8.

The invention also provides a vision absolute type rotation angle measuring method, which adopts the measuring device to measure; the measuring method comprises the following steps:

step 1, calibrating the measuring device to obtain calibration data, wherein the calibration data comprises a gray scale centroid coordinate of a gray scale identifier of each gray scale level and a corresponding angle value;

step 2, shooting an image through a CCD camera;

step 3, processing the image shot by the CCD camera to obtain the gray scale centroid coordinate of the gray scale identifier in the image, and calculating the average gray scale value of the gray scale identifier in the image;

step 4, determining the gray level of the gray identification according to the average gray value of the gray identification in the image, and further obtaining the corresponding angle value ang of the gray identification in the calibration data;

step 5, finding a left side gray scale identifier pa and a right side gray scale identifier pb which are closest to the gray scale identifier pa in the calibration data according to the gray scale centroid coordinates of the gray scale identifiers in the image;

step 6, calculating an included angle dela _ ang of the left gray mark pa and the right gray mark pb according to the angle values corresponding to the two gray marks in the calibration data and the angle ratio b: c of the two gray marks;

and 7, estimating the actual rotation angle pt by using linear interpolation, wherein the estimation formula is as follows:

the rotation angle + dela _ ang × b/(b + c) corresponding to pt ═ pa corresponds to the rotation angle-dela _ ang × c/(b + c) corresponding to pb;

and 8, calculating the current absolute rotation angle as ang + pt.

Further, the method for calibrating the measuring device to obtain calibration data in step 1 comprises:

step 11, randomly selecting a gray mark, and setting the gray mark as a rotation zero position when the gray mark is at a certain position in a CCD camera shooting visual field;

step 12, rotating the code disc to enable the gray mark to completely pass through the CCD camera shooting visual field; in the moving process of the gray scale identifier, shooting images In at intervals by a CCD camera, and acquiring an angle value corresponding to the moment of shooting the images In by a standard rotation angle measuring device;

step 13, processing the images In sequence:

(1) dividing the image into binary images by using a fixed threshold, wherein the gray scale in the binary images is marked as a white area, and the background is a black area;

(2) calculating the number of the white areas, and if the number of the white areas is equal to 1, directly selecting the white areas; if the number of the white areas is more than 1, calculating the area of each white area, and if the area difference of each white area is more than or equal to a set value a, selecting the white area with the largest area, otherwise, selecting the white area at the edge of the binary image;

(3) acquiring image coordinates of all pixels in the selected white area, extracting gray values of all pixels on the original image according to the image coordinates, and then calculating gray centroid coordinates of gray identifiers in the current image;

(4) recording a gray scale centroid coordinate of a gray scale identifier in a current image and a corresponding angle value;

(5) repeating the steps (1) to (4) to finish processing all the images In, and obtaining the gray scale centroid coordinates of the gray scale marks In all the images In and the corresponding angle values;

and 14, repeating the steps 11 to 13 for each gray scale identifier, and recording the gray scale centroid coordinate and the corresponding angle value of the gray scale identifier of each gray scale level as calibration data.

Further, the method for processing the image shot by the CCD camera in step 3 to obtain the gray scale centroid coordinate of the gray scale identifier in the image is:

(3) and acquiring the image coordinates of all pixels in the selected white area, extracting the gray values of all pixels on the original image according to the image coordinates, and then calculating the coordinates of the center of mass of the gray values.

In summary, due to the adoption of the technical scheme, the invention has the beneficial effects that:

1. the measuring device only needs to use an industrial-grade CCD camera, the code disc can be printed quickly at low cost by using a modern printing technology, and compared with the traditional grating, the manufacturing process complexity, the processing time and the cost are obviously reduced.

2. The measuring device has absolute positioning capability and can directly obtain the angle between the current position and the zero point position.

3. The gray scale mark on the code disc of the measuring device is not necessarily based on glass-based quality, can be more suitable for non-light-transmitting materials such as metal and the like, is natural and high in reliability, and has impact resistance and vibration resistance.

4. The measuring device has extremely small rotation angle measuring resolution, even continuous measuring capability, and is more precise than the traditional grating measurement.

5. The measuring device provided by the invention has lower processing and mounting precision, does not need excessively high processing and assembling requirements such as concentricity, coaxiality and planeness, and is suitable for batch production.

6. The measuring method has the characteristics of low operation complexity and capability of carrying out high-frequency measurement.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present invention, and therefore should not be considered as limiting the scope, and for those skilled in the art, other related drawings can be obtained according to the drawings without inventive efforts.

FIG. 1 is a schematic structural diagram of a code wheel of the absolute visual rotation angle measuring device of the present invention.

Fig. 2 is a schematic structural diagram of the absolute visual rotation angle measuring apparatus according to the present invention.

FIG. 3 is a block diagram of a method for measuring a visual absolute rotation angle according to the present invention.

FIG. 4 is a schematic diagram of movement of grayscale markers during calibration in the absolute visual rotation angle measurement method of the present invention.

Icon: 1-CCD camera, 2-code disc, 3-gray scale mark and 4-rotating shaft.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. The components of embodiments of the present invention generally described and illustrated in the figures herein may be arranged and designed in a wide variety of different configurations.

Thus, the following detailed description of the embodiments of the present invention, presented in the figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of selected embodiments of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Examples

As shown in fig. 1-2, the present embodiment provides a visual absolute type rotation angle measuring device, which includes a CCD camera 1 and an annular code wheel 2, wherein the middle of the code wheel 2 rotates through a connecting rotating shaft 4;

n co-circular gray scale marks 3 are uniformly distributed on the ring of the code disc 2, and the gray scale value of each gray scale mark 3 corresponds to n-level gray scale values which are set at uniform intervals in a gray scale value interval of 0-255;

the CCD camera 1 is arranged above the code disc 2, so that the shooting visual field of the CCD camera is aligned to the gray scale mark 3, and at least one complete gray scale mark 3 exists in the shooting visual field at any moment.

The invention is further illustrated by taking n-8 as an example, and referring to fig. 1, the gray marks 3 are 8 in total, are solid circles of different gray values, and are all circular. The 8 gray marks 3 are numbered as 0, 1, 2, 3, 4, 5, 6 and 7 in sequence from deep to light. In the interval of 0-255 gray-scale values, the following intervals are adopted to set 0-7 levels (total n is 8 levels) of gray-scale values, and the following are sequentially adopted:

0，32，64，96，128，160，192，224

in order to make the difference between the gray values of the adjacent gray marks 3 large, the gray values of the adjacent gray marks 3 are generally different by at least 2 gray values, and thus, the 8 gray marks 3 can be arranged in a cycle as follows:

8-1-5-2-6-3-7-4 (number 4 is adjacent to number 8 gray scale mark 3)

If 0 is taken as a rotation zero point, the corresponding angles of the 8 gray marks 3 are as follows:

0，45，90，135，180，225，270，315

based on the above-mentioned vision absolute type rotation angle measuring apparatus, this embodiment further provides a vision absolute type rotation angle measuring method, as shown in fig. 3, the measuring method includes the following steps:

step 1, calibrating the measuring device to obtain calibration data, wherein the calibration data comprises a gray scale centroid coordinate and a corresponding angle value of a gray scale identifier 3 of each gray scale level;

when the measuring device is assembled for the first time, calibration is needed, and in the calibration process, an actual rotating angle value is output according to a standard rotating angle measuring device and is used as a real rotating value. Specifically, the method for calibrating the measuring device to obtain calibration data comprises the following steps:

step 11, arbitrarily selecting one gray mark 3, and setting the gray mark as a rotation zero position when the CCD camera 1 shoots a certain position in the visual field, as shown in FIG. 4;

step 12, rotating the code disc 2 to enable the gray scale mark 3 to completely pass through the shooting view field of the CCD camera 1; in the moving process of the gray scale mark 3, the CCD camera 1 is used for shooting images In at intervals, and an angle value (the anticlockwise direction can be set as positive, and the clockwise direction is changed into negative) corresponding to the moment of shooting the images In is obtained through a standard rotating angle measuring device;

step 13, processing the images In sequence:

(1) dividing the image into binary images by using a fixed threshold, wherein the gray scale marks 3 in the binary images are white areas, and the background is a black area;

(2) calculating the number of the white areas, and if the number of the white areas is equal to 1, directly selecting the white areas; if the number of the white areas is more than 1, calculating the area of each white area, and when the area difference of each white area is more than or equal to a set value a, selecting the white area with the largest area, otherwise, selecting the white area at the most edge (the leftmost side or the rightmost side, and each selection criterion must be consistent) in the binary image; the value a is selected according to the imaging characteristics of the CCD camera 1 by experience, and whether the gray mark 3 is complete or not can be correctly identified;

(3) acquiring image coordinates of all pixels in the selected white area, extracting gray values of all pixels on the original image according to the image coordinates, and then calculating a gray centroid coordinate of a gray identifier 3 in the current image;

(4) recording the gray scale centroid coordinates and the corresponding angle values of the gray scale identification 3 in the current image;

(5) repeating the steps (1) to (4) to finish processing all the images In, and obtaining the gray scale centroid coordinates and the corresponding angle values of the gray scale identifiers 3 In all the images In;

and 14, repeating the steps 11 to 13 for each gray scale identifier 3, and recording the gray scale centroid coordinates and the corresponding angle values of the gray scale identifiers 3 of each gray scale level as calibration data. In step 14, because any gray scale marker 3 on the code wheel 2 has the same motion track on the image, or the generated motion track error is within the allowable range, each gray scale marker 3 is calibrated independently through step 14, so that the measurement accuracy can be further improved, or the misalignment of the marker motion tracks caused by micro-deformation of the code wheel 2 can be compensated.

And when the calibration is finished, performing the measurement mode of the steps 2-6:

step 2, shooting an image through the CCD camera 1;

step 3, processing the image shot by the CCD camera 1 to obtain the gray scale centroid coordinate of the gray scale identifier 3 in the image, and calculating the average gray scale value of the gray scale identifier 3 in the image; the method for processing the image shot by the CCD camera 1 to obtain the gray scale centroid coordinate of the gray scale identifier 3 in the image is consistent with the calibration process, and comprises the following steps: (1) dividing the image into binary images by using a fixed threshold, wherein the gray scale marks 3 in the binary images are white areas, and the background is a black area;

Step 4, determining the gray level of the gray mark 3 according to the average gray value of the gray mark 3 in the image, and further obtaining the corresponding angle value ang of the gray mark 3 in the calibration data;

step 5, finding a left side gray scale identifier 3pa and a right side gray scale identifier 3pb which are closest to the gray scale identifier 3 in the calibration data according to the gray scale centroid coordinate of the gray scale identifier 3 in the image;

step 6, calculating an included angle dela _ ang of the left gray mark 3pa and the right gray mark 3pb according to the corresponding angle values of the two and the angle ratio b: c of the two;

and 8, calculating the current absolute rotation angle as ang + pt.

It can be seen from the above that, the method and device for measuring a visual absolute rotation angle of the present invention have the following advantages:

1. the measuring device only needs to use the industrial-grade CCD camera 1, the code disc 2 can use the modern printing technology, the cost is low, the printing is rapid, and compared with the traditional grating, the manufacturing process complexity, the processing time and the cost are obviously reduced.

3. The gray scale mark 3 on the coded disc 2 of the measuring device is not necessarily based on glass-based quality, can be more suitable for non-light-transmitting materials such as metal and the like, is natural and high in reliability, and has impact resistance and vibration resistance.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A visual absolute type rotation angle measuring device is characterized by comprising a CCD camera and an annular coded disc, wherein the middle part of the coded disc rotates through a connecting rotating shaft;

2. The vision absolute rotation angle measuring method and apparatus of claim 1, wherein the gray values of adjacent gray marks differ by at least 2 gray values.

3. The absolute rotary vision angle measuring device of claim 2, wherein the gray scale markings are solid circles.

4. The absolute visual angle measuring device of claim 3, wherein n is 8.

5. A visual absolute rotation angle measuring method characterized by performing measurement using the measuring apparatus according to any one of claims 1 to 4; the measuring method comprises the following steps:

step 2, shooting an image through a CCD camera;

and 8, calculating the current absolute rotation angle as ang + pt.

6. The vision absolute type rotation angle measuring method according to claim 5, wherein the method of calibrating the measuring device to obtain calibration data in step 1 is:

step 13, processing the images In sequence:

7. The vision absolute rotation angle measuring method of claim 6, wherein the step 3 of processing the image captured by the CCD camera to obtain the coordinates of the center of mass of the gray scale marker in the image comprises: