阅读说明：本技术 一种基于绝对位置旋转型编码器的角位移视觉测量方法 (Angular displacement visual measurement method based on absolute position rotary encoder ) 是由 雷经发 陈志强 孙虹 张淼 李永玲 刘涛 韦旺 何玉 于 2020-03-19 设计创作，主要内容包括：本发明公开了一种绝对位置旋转型编码器的角位移视觉测量方法,该方法采用边沿高度连续变化且与角度成正比关系的绝对位置旋转型编码器,用激光笔平行于旋转型编码器中心轴照射并使得激光点落在边沿上,然后采用一台已知内部参数的相机从任意角度拍摄,保证完整拍到激光点即可,接着运用图像处理技术得到激光点的像点,再根据系统标定结果和相机成像模型解算出激光点在世界坐标系下的位置,最后根据比例关系即可换算出当前此旋转型编码器旋转的角位移。本发明相比现有技术具有以下优点：该方法能够解决掉电情况下绝对角位移丢失情况,且可提供一种非接触、高分辨率、高精度的角位移测量方案。(The invention discloses an angular displacement visual measurement method of an absolute position rotary encoder, which adopts the absolute position rotary encoder with continuously changing edge height and proportional relation with angle, uses a laser pen to irradiate in parallel with the central shaft of the rotary encoder and make a laser point fall on the edge, then adopts a camera with known internal parameters to shoot from any angle, ensures that the laser point is completely shot, then uses image processing technology to obtain an image point of the laser point, then calculates the position of the laser point under a world coordinate system according to a system calibration result and a camera imaging model, and finally can convert the current rotary angular displacement of the rotary encoder according to the proportional relation. Compared with the prior art, the invention has the following advantages: the method can solve the problem of absolute angular displacement loss under the condition of power failure, and can provide a non-contact, high-resolution and high-precision angular displacement measurement scheme.)

1. An angular displacement vision measurement method based on an absolute position rotary encoder is characterized by comprising the following steps:

s1, constructing an angular displacement visual measurement world coordinate system based on a pre-designed absolute position rotary encoder, and acquiring first light spot data with a known height value by adopting an image acquisition device;

s2, obtaining image point coordinates (u, v) by the first light spot with known Z coordinates through least square fitting, and calibrating and solving second light spot data to calculate the coordinates of the second light spot data in a world coordinate system XY plane;

s3, fitting the coordinates (u) of the image point of the second light point by a least square method₂,v₂) Calculating the height direction data of the second light spot in the world coordinate system by combining the calibration result;

and S4, converting the absolute angular displacement of the rotary encoder into absolute angular displacement according to the proportional relation between the height and the angle to finish measurement.

2. A method of visual measurement of angular displacement based on an absolute position rotary encoder according to claim 1, wherein said pre-designed absolute position rotary encoder is embodied as a rotary encoder with continuously varying edge height and proportional angle, wherein the relationship between edge height H and angle θ is as follows:

in the formula, h₁Is the height of the lowest edge of the rotary encoder, and the corresponding maximum angle is theta₁，h₂Is the height of the highest position of the edge, and the corresponding minimum angle is theta₂。

3. A method of visual measurement of angular displacement based on an absolute position rotary encoder according to claim 2, wherein said world coordinate system is embodied as: the origin O point of the world coordinate system is in the same point with the central point of the rotary encoder chassis, the XY plane of the world coordinate system is coplanar with the plane of the rotary encoder chassis, and the Z axis is parallel to the light.

4. The method of claim 3, wherein the step of obtaining the first light spot data with a known height value by using the image capturing device comprises: and (3) irradiating by using a laser pen parallel to the central shaft of the rotary encoder and enabling a laser point to always fall on the edge to form first light spot data, wherein the height value of the first light spot data is known.

5. A visual measurement of angular displacement based on an absolute position rotary encoder according to claim 4, wherein said image capturing means comprises a camera with known internal parameters.

6. The method of visually measuring an angular displacement based on an absolute position rotary encoder according to claim 5, wherein said step S2 specifically comprises:

step s201, calibrating R, T according to the linear imaging model by acquiring the first light spot data with known height value Z, as follows:

where ρ is a scale factor, [ x, y, z,1 [ ]]^TThe homogeneous coordinate of the calibration point on the calibration plate under the world coordinate system is obtained; [ m, n,1 ]]^THomogeneous coordinates of the index point image points; k is an internal parameter of the camera, wherein,α_u、α_vscale factors on u and v axes of the image respectively; u. of₀、v₀Is the geometric center of the picture;

wherein [ r ]₁r₂r₃]A column vector of R, satisfying the following relationship:

in the formula, "| | | non-conducting phosphor₂"represents the modulus of the vector," · "represents the vector inner product;

s202, calibrating the second light spot by constructing a linear equation set according to the calibration result and the camera imaging model and solving a horizontal and vertical coordinate x under the XY plane of the world coordinate system_l，y_lThe values are shown below:

order:

a system of linear equations is obtained:

calibrating the abscissa x of the second spot according to the above formula_l，y_lThe value of (c).

7. The method of claim 6 wherein the fitting of the coordinates (u) of the image point of the second spot is performed by least squares₂,v₂) And calculating the height direction data of the second light spot under the world coordinate system by combining the calibration result, which specifically comprises the following steps: based on the horizontal and vertical coordinates x_l，y_lThe height value is obtained according to the following formula:

order:then the following results are obtained:

thus, the z of the light spot is determined_pValue, wherein z of the light spot_pThe value is the height value H of the edge where the second light spot is located after the rotary encoder rotates.

8. A visual measurement of angular displacement of a rotary encoder based on absolute position and rotation type as claimed in claim 7, wherein said scaling to absolute angular displacement of the rotary encoder based on the proportional relationship of height to angle comprises obtaining absolute angular displacement θ based on the obtained height H as:

9. the method of claim 8, wherein the image capturing device further comprises a laser pointer for capturing spot data by irradiating parallel to the central axis of the rotary encoder.

10. A method of visual measurement of angular displacement of an absolute position-based rotary encoder according to claim 8, wherein said rotary encoder rotates 360 ° in one revolution.

Technical Field

The invention relates to the technical field of camera calibration, in particular to an angular displacement visual measurement method of an absolute position rotary encoder.

Background

An encoder is an angular position sensing measuring device that converts a physical signal into an electrical signal that can be communicated, transmitted and stored by dividing the spatial position with a certain regular code, and can be used to measure angular or linear displacements, the former being called code wheels and the latter being called code rulers. The encoder is connected with a computer and a display device to realize dynamic measurement and real-time control, has the advantages of simple structure, high resolution, high precision, easy maintenance and the like, is widely applied to various fields of national defense, aerospace, robots, numerical control, digital display systems and the like, and has great application value.

Conventional encoders can be classified into an incremental type and an absolute type according to differences in operation principles. The coded disc of the incremental encoder has uniform coding intervals, and the principle is that collected pulse signals are accumulated relative to a reference zero position, positive rotation is performed for increasing, and negative rotation is performed for decreasing. The absolute encoder divides the code disc into a plurality of sector areas, each sector area corresponds to a unique code, so that the absolute encoder does not need to be calibrated again after power failure, and the absolute encoder has the advantages of strong anti-interference capability and the like, but the resolution of measuring angular displacement is limited by the number of the sector areas, the manufacturing process is complex, and the application range of the absolute encoder is influenced. On the other hand, the working modes of the two encoders require auxiliary equipment to convert photoelectric pulse signals into coded information for measurement, so that the resolution is limited, and a complicated equipment installation process is increased.

Disclosure of Invention

The invention aims to overcome the defects of the prior art, provides an angular displacement vision measurement method of an absolute position rotary encoder, aims to solve the technical problem of recalibration of a reference zero position under the condition of power failure and restarting, and provides a non-contact high-resolution and high-precision angular displacement measurement scheme.

According to an embodiment of the present invention, the present invention provides an angular displacement vision measuring method based on an absolute position rotary encoder, comprising the steps of:

s1, constructing an angular displacement visual measurement world coordinate system based on a pre-designed absolute position rotary encoder, and acquiring first light spot data with a known height value by adopting an image acquisition device;

s2, obtaining image point coordinates (u, v) by the first light spot with known Z coordinates through least square fitting, and calibrating and solving second light spot data to calculate the coordinates of the second light spot data in a world coordinate system XY plane;

s3, fitting the image point coordinate (u) of the second light point by a least square method₂,v₂) Calculating the height direction data of the second light spot in the world coordinate system by combining the calibration result;

and S4, converting the absolute angular displacement of the rotary encoder into absolute angular displacement according to the proportional relation between the height and the angle to finish measurement.

Preferably, the pre-designed absolute position rotary encoder is a rotary encoder with continuously changing edge height and proportional angle, wherein the relationship between the edge height H and the angle θ is as follows:

in the formula, h₁Is the height of the lowest edge of the rotary encoder, and the corresponding maximum angle is theta₁，h₂Is the height of the highest point of its edge, whichCorresponding to a minimum angle of theta₂。

Preferably, the world coordinate system is specifically: the origin O point of the world coordinate system is in the same point with the central point of the rotary encoder chassis, the XY plane of the world coordinate system is coplanar with the plane of the rotary encoder chassis, and the Z axis is parallel to the light.

Preferably, the acquiring of the first light spot data with a known height value by using the image acquisition device is to irradiate the laser pointer parallel to the central axis of the rotary encoder and make the laser spot always fall on the edge to form the first light spot data, where the height value of the first light spot data is known.

Preferably, the step S2 specifically includes:

step s201, calibrating R, T according to the linear imaging model by acquiring the first light spot data with known height value Z, as follows:

where ρ is a scale factor, [ x, y, z,1 [ ]]^TThe homogeneous coordinate of the calibration point on the calibration plate under the world coordinate system is obtained; [ m, n,1 ]]^THomogeneous coordinates of the index point image points; k is an internal parameter of the camera, wherein,α_u、α_vscale factors on the u and v axes of the image or normalized focal length; u. of₀、v₀Is the geometric center of the picture;

wherein [ r ]₁r₂r₃]A column vector of R, satisfying the following relationship:

in the formula, "| | | non-conducting phosphor₂"represents the modulus of the vector," · "represents the vector inner product;

s202, calibrating the second light spot by constructing a linear equation set according to the calibration result and the camera imaging model and solving a horizontal and vertical coordinate x under the XY plane of the world coordinate system_l，y_lThe values are shown below:

order:

a system of linear equations is obtained:

calibrating the abscissa x of the second spot according to the above formula_l，y_lThe value of (c).

Preferably, the fitting of the coordinates (u) of the image point of the second light point by means of a least squares method₂,v₂) And calculating the height direction data of the second light spot under the world coordinate system by combining the calibration result, specifically based on the horizontal and vertical coordinates x_l，y_lThe height value is obtained according to the following formula:

order: then the following results are obtained:

thus, the z of the light spot is determined_pValue, wherein z of the light spot_pThe value is the height value H of the edge where the second light spot is located after the rotary encoder rotates.

Preferably, said performing the measurement in terms of the proportional relationship between the height and the angle as converted into the absolute angular displacement of the rotary encoder comprises obtaining the absolute angular displacement θ as:

preferably, the image capturing device comprises a camera with known internal parameters.

The image acquisition device also comprises a laser pen which is used for irradiating parallel to the central shaft of the rotary encoder to acquire light spot data.

Preferably, the rotary-type encoder rotates 360 ° once.

Compared with the prior art, the invention has the following advantages: the image processing target is clear, the image point is easy and quick to obtain, and the image processing is simple and does not need a complex algorithm because only the image coordinate of the laser point needs to be obtained, so that the speed is high, and the real-time measurement can be realized; the edge height of the absolute position rotary encoder is continuously changed, so that the absolute position rotary encoder has high angular displacement measurement resolution and cannot lose absolute angular displacement after power failure; the photographic technology is applied to angular displacement measurement, and calibration is not needed to be carried out again once, so that the requirement of equipment is reduced, and a non-contact measurement method is provided, so that the interference to an object is reduced; the whole process is simple in algorithm, and the requirement of computing equipment is lowered. Compared with the existing method, the absolute position rotary encoder angular displacement measurement method based on monocular vision provided by the invention has the characteristics of non-contact, high resolution, simple calibration, absolute position and high precision, and has great practical application value.

Drawings

FIG. 1 is a flow chart of a visual measurement method of angular displacement based on an absolute position rotary encoder according to the present invention;

FIG. 2 is a schematic structural view of an angular displacement vision measuring method based on an absolute position rotary encoder according to the present invention

FIG. 3 is a schematic diagram of a coordinate system of an angular displacement vision measurement method based on an absolute position rotary encoder according to the present invention;

FIG. 4 is a diagram of an embodiment of a visual angular displacement measurement method based on an absolute position rotary encoder according to the present invention;

FIG. 5 is a diagram of a visual measurement method of angular displacement based on an absolute position rotary encoder according to another embodiment of the present invention.

Detailed Description

The following examples are given for the detailed implementation and specific operation of the present invention, but the scope of the present invention is not limited to the following examples.