Device and method for measuring flatness of plane by using RFID (Radio Frequency Identification Device)

Abstract

The invention discloses a device and method for measuring the flatness of a plane by using RFID, and relates to the technical field of RFID positioning, and the device comprises a horizontal slide way, a vertical slide way is arranged on the side wall of one end of the horizontal slide way in a penetrating manner, and a reader-writer slide rod is arranged in one side of the vertical slide way. A radio frequency identification sliding rod matched with the reader-writer sliding rod is arranged in the other side of the vertical sliding way, and a movable assembly is arranged at the bottom of the radio frequency identification sliding rod. The device is simple in design and easy to process and assemble, can provide a high-precision flatness measurement result through accurate distance measurement and geometric calculation, is more economical and practical compared with traditional measurement equipment, is allowed to be easily carried by a user due to the size and weight, is suitable for field measurement, and is suitable for popularization and application. The method can achieve the plane flatness measurement of a large-area product, and is suitable for various application scenes.

Description

Technical Field

[0001] The present invention relates to the technical field of RFID positioning, and in particular to a device and method for measuring the flatness of a plane using RFID. Background Art

[0002] With the continuous improvement of the world's industrial system, the requirements for the shape errors of industrial products are also constantly increasing. Under this general trend, higher requirements are placed on the accuracy of measuring instruments for plane flatness (a type of shape tolerance that includes indicators such as parallelism and straightness tolerance).

[0003] At present, the equipment for measuring the shape error of the surface of parts is expensive, too large and bulky to be carried, and the measurement range is small when multiple shape tolerances are measured together, so the flatness of a single large-area object surface cannot be measured. In addition, the failure rate of traditional optical measuring instruments is high, and the energy consumption is large. They are not suitable for use in scenarios with complex working conditions and easy portability. The traditional mechanical caliper measurement structure tester is estimated by the naked eye, resulting in an error of usually around 50um to 200um, which cannot meet the needs of the growing high-precision measurement. In addition, the mechanical caliper is not convenient for storing and analyzing large amounts of data, and is not suitable for analysis with modern data processing applications. In addition, the service life of traditional testing equipment is low due to material fatigue loss, sliding wear, improper operation and other instrument damage. However, RFID equipment reduces the requirements for the instrument itself through origin correction and principle calculation, which greatly improves the service life of the equipment.

[0004] Currently, no effective solution has been proposed for the problems in the related technologies. Summary of the invention

[0005] In view of the problems in the related art, the present invention proposes a device and method for measuring the flatness of a plane using RFID to overcome the above technical problems existing in the existing related art.

[0006] To this end, the specific technical solution adopted by the present invention is as follows:

[0007] According to one aspect of the present invention, a device for measuring the flatness of a plane using RFID is provided, comprising a horizontal slide, a vertical slide is provided through the side wall of one end of the horizontal slide, a reader-writer slide is provided inside one side of the vertical slide, a radio frequency identification slide that cooperates with the reader-writer slide is provided inside the other side of the vertical slide, and a movable component is provided at the bottom of the radio frequency identification slide.

[0008] Furthermore, a directional reader is arranged on one side wall of the top of the reader-writer slide bar, and a radio frequency tag is symmetrically arranged on one side wall of the top of the radio frequency identification slide bar.

[0009] Furthermore, both side walls of the vertical slideway are symmetrically provided with slide grooves matching with the movable components.

[0010] Furthermore, a moving groove matching with the vertical slideway is provided on one side of the horizontal slideway.

[0011] Furthermore, the movable component includes fixed plates symmetrically arranged on the side walls at both ends of the bottom of the RFID slide bar, a movable ball is arranged between the bottoms of the two fixed plates, and a movable plate is arranged on the side wall at one end of the top of the fixed plate.

[0012] Furthermore, the side walls at one end of the movable plate are symmetrically provided with sliding columns that match the sliding grooves.

[0013] According to another aspect of the present invention, a method for measuring the flatness of a surface using RFID is provided. The method for measuring the flatness of a surface using RFID comprises the following steps:

[0014] S1. Set the coordinate origin and use the radio frequency identification ranging principle to quantify the transmission power;

[0015] S2, move the RFID slider to the measuring point on the plane to be measured, record the plane coordinates of the measuring point at this time according to the moving distance in the horizontal and vertical directions, turn on the directional reader, obtain the distance between the directional reader and the two RFID tags, calculate the vertical distance difference of the measuring point according to the plane geometry, and record the three-dimensional coordinate data of the measuring point;

[0016] S3. Repeat step S2 to record the three-dimensional coordinate data of each measuring point. Record the three-dimensional coordinate data of all measuring points in a table and upload it to the analysis software. Generate a plane flatness image through data processing to intuitively display the flatness distribution.

[0017] Furthermore, setting the coordinate origin and using the radio frequency identification ranging principle to quantify the transmission power includes the following steps:

[0018] S11, start the directional reader, configure the transmission power, transmission gain and working wavelength of the directional reader, and confirm the activation power of the radio frequency tag;

[0019] S12, setting the directional reader and the radio frequency tag at a preset reference distance, and using a power calculation formula to calculate the power received by the radio frequency tag at the preset reference distance;

[0020] S13, move the directional reader to any point to be tested, measure the power received by the radio frequency tag, and calculate the actual distance between the directional reader and the radio frequency tag.

[0021] Furthermore, the power calculation formula is:

[0022]

[0023] Where P t represents the power received by the RFID tag at the preset reference distance; λ represents the working wavelength of the RFID tag; τ represents the power transmission coefficient; P r Indicates the transmission power of the directional reader; G r Represents the transmission gain of the directional reader; G t represents the gain of the RFID tag; l represents the distance between the RFID tag and the directional reader.

[0024] Furthermore, the formula for the vertical distance difference of the measuring points calculated by plane geometry is:

[0025]

[0026] In the formula, d represents the vertical distance difference; l0 represents the distance between two RFID tags; l1 and l2 both represent the distance between the directional reader and the RFID tag.

[0027] The beneficial effects of the present invention are:

[0028] 1. The present invention has a simple design and is easy to process and assemble. It can provide high-precision flatness measurement results through precise distance measurement and geometric calculation. It is more economical than traditional measuring equipment. The size and weight of the device for measuring plane flatness allow users to carry it easily, which is suitable for on-site measurement. It can realize the plane flatness measurement of large-area products and is suitable for a variety of application scenarios.

[0029] 2. The present invention can be combined with a digital control system to achieve automatic sampling and data recording, and data processing and image drawing can be performed through software such as Matlab, which is convenient for analysis and evaluation. The RFID technology and modern signal processing methods, such as interpolation, are used to improve the accuracy and reliability of measurement. Due to the simple structure, daily maintenance and calibration are easier, making the present invention have potential application value in the field of industrial measurement, especially in situations where high-precision and portable measurement tools are required. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0031] Figure 1 is a three-dimensional diagram of a device for measuring plane flatness using RFID according to an embodiment of the present invention;

[0032] Figure 2 is a cross-sectional view of a device for measuring plane flatness using RFID according to an embodiment of the present invention;

[0033] Figure 3 is a three-dimensional diagram from another angle of a device for measuring plane flatness using RFID according to an embodiment of the present invention;

[0034] Figure 4 is a schematic diagram of solving the vertical distance difference according to an embodiment of the present invention;

[0035] Figure 5 is a sampling point data graph available for analysis after being processed by the interpolation method according to an embodiment of the present invention;

[0036] Figure 6 The figure is a flow chart of a method for measuring plane flatness by using RFID according to an embodiment of the present invention.

[0037] In the figure:

[0038] 1. Horizontal slide; 2. Vertical slide; 3. Reader / writer slide bar; 4. RFID slide bar; 5. Movable component; 501. Fixed plate; 502. Movable ball; 503. Movable plate; 504. Slide column; 6. Directional reader / writer; 7. RFID tag; 8. Slide slot; 9. Moving slot. DETAILED DESCRIPTION

[0039] To further illustrate each embodiment, the present invention provides drawings, which are part of the disclosure of the present invention and are mainly used to illustrate the embodiments and can be used in conjunction with the relevant descriptions in the specification to explain the operating principles of the embodiments. With reference to these contents, ordinary technicians in the field should be able to understand other possible implementations and advantages of the present invention. The components in the figures are not drawn to scale, and similar component symbols are generally used to represent similar components.

[0040] According to an embodiment of the present invention, a device and method for measuring the flatness of a plane using RFID are provided.

[0041] The present invention will now be further described with reference to the accompanying drawings and specific embodiments. Figure 1-Figure 3 As shown, the device for measuring the flatness of a plane using RFID according to an embodiment of the present invention includes a horizontal slide 1 (i.e., the slide in the X direction), a vertical slide 2 (i.e., the slide in the Y direction) is penetrated through the side wall of one end of the horizontal slide 1, a reader / writer slide 3 (i.e., the PCD slide) is arranged inside one side of the vertical slide 2, a radio frequency identification slide 4 (i.e., the RFID slide) matched with the reader / writer slide 3 is arranged inside the other side of the vertical slide 2, and a movable component 5 is arranged at the bottom of the radio frequency identification slide 4.

[0042] In this optional embodiment, a directional reader / writer 6 is disposed on one side wall of the top of the reader / writer slide bar 3 , and a radio frequency tag 7 (ie, RFID tag) is symmetrically disposed on one side wall of the top of the radio frequency identification slide bar 4 .

[0043] In this optional embodiment, both end side walls of the vertical slideway 2 are symmetrically provided with slide grooves 8 that cooperate with the movable component 5 .

[0044] In this optional embodiment, a moving groove 9 matching with the vertical slideway 2 is provided on one side of the horizontal slideway 1 .

[0045] In this optional embodiment, the movable component 5 includes fixed plates 501 symmetrically arranged on the side walls at both ends of the bottom of the RFID slide bar 4, a movable ball 502 is arranged between the bottoms of the two fixed plates 501, and a movable plate 503 is arranged on the side walls at one end of the top of the fixed plates 501.

[0046] In this optional embodiment, the side walls at one end of the movable plate 503 are symmetrically provided with sliding posts 504 that cooperate with the sliding grooves 8.

[0047] According to another embodiment of the present invention, Figure 6 As shown, a method for measuring the flatness of a surface using RFID is also provided. The method for measuring the flatness of a surface using RFID comprises the following steps:

[0048] S1. Set the coordinate origin and use the radio frequency identification ranging principle to quantify the transmission power;

[0049] S2, move the RFID slider 4 to the measuring point on the plane to be measured, record the plane coordinates of the measuring point at this time according to the moving distance in the horizontal direction and the vertical direction, turn on the directional reader 6, obtain the distance between the directional reader 6 and the two RFID tags 7, and calculate the vertical distance difference of the measuring point according to the plane geometry, and record the three-dimensional coordinate data of the measuring point;

[0050] It needs to be explained that Figure 4 As shown, the RFID slider (i.e., radio frequency identification slider 4) in the device is placed at a certain position to be measured, and the plane coordinates (X, Y) of the sampling point at this time are recorded according to the moving distance in the X and Y directions. The distance measurement function is turned on to calculate the distances l1 and l2 between the directional reader 6 (PCD) and the two tags (i.e., the two radio frequency tags 7). At this time, since the three sides l0, l1, and l2 of the triangle ABC are all known, the vertical change distance d (vertical distance difference) at this time can be calculated based on the relevant knowledge of plane geometry. The calculation steps are as follows:

[0051]

[0052] Wherein, l0 represents the distance between two RFID tags; l1 and l2 both represent the distance between the directional reader and the RFID tag; from the above formula, it can be obtained that d=l2cosθ-l0 (i.e., the vertical distance difference formula of the plane geometry calculation measurement point in the present invention).

[0053] S3. Repeat step S2 to record the three-dimensional coordinate data of each measuring point. Record the three-dimensional coordinate data of all measuring points in a table and upload it to the analysis software. Generate a plane flatness image through data processing to intuitively display the flatness distribution.

[0054] It needs to be explained that Figure 5 As shown, after combining the vertical distance difference of this point (i.e., the measurement point) with the plane coordinates to obtain (X, Y, Z), the device can be placed at other points in the test area by a digital control system or manually for sampling, and the data can be automatically or manually recorded and uploaded to the analysis software for analysis. As shown in Table 1, it is an example table of the coordinates of 25 sampling points and their vertical distance differences obtained in one measurement.

[0055] Table 1: Example table of sampling point coordinates and their vertical distance differences

[0056] (1，1，0) (2，1，0) (3，1，0) (4，1，0) (5，1，0) (1，2，0) (2，2，0) (3，1，0) (4，1，0) (5，1，0) (1，3，0) (2，3，0) (3，1，0) (4，1，0) (5，1，0) (1，4，0) (2，4，0) (3，1，0) (4，1，0) (5，1，0) (1，5，0) (2，5，0) (3，1，0) (4，1，0) (5，1，0)

[0057] It should be explained that the present invention provides a method for processing data using Matlab and drawing an image. An example of a Matlab acquisition point data processing program is as follows:

[0058] % Example data points (x, y, z), here we assume that we already have our own data points

[0059] x=[1,1,1,1,1,2,2,2,2,2,3,3,3,3,3,4,4,4,4,4,5,5,5,5,5];

[0060] y=[1,2,3,4,5,1,2,3,4,5,1,2,3,4,5,1,2,3,4,5,1,2,3,4,5];

[0061] z=[0,0.01,0.02,0.02,0,0,0,0.09,0.15,0.09,0.01,0.03,0.01,0.02,0.01,0.02,0.03,0.01,0,0,0.08,0,0,0,0];

[0062] %Define the interpolation grid

[0063] [X, Y]=meshgrid(min(x):0.1:max(x),min(y):0.1:max(y));

[0064] % Interpolation

[0065] z=griddata(x,y,z,X,Y,'cubic');

[0066] % Plot the original data points

[0067] scatter3(x,y,z,'filled');

[0068] hol don;

[0069] %Draw the interpolated binary function image

[0070] surf(X, Y, Z);

[0071] hold off;

[0072] %Set to black and white color mapping

[0073] colormap(gray);

[0074] %Set graphic properties

[0075] xlabel('X axis');

[0076] ylabel('Y axis');

[0077] zlabe1('z axis');

[0078] title('Binary function image of vertical distance difference d about sampling points (X, Y)');

[0079] % Add color bar

[0080] colorbar;tyu 7

[0081] It needs to be explained that regarding the selection of sampling points: the number of sampling points determines the test accuracy. The device can be installed with a PLC control system, and the sampling interval and the number of samples can be input to automatically perform sampling. And the sampling process is divided into uniform sampling and non-uniform sampling: if the distance between every two sampling points is constant in a uniform distribution, it is suitable for measuring unknown surface characteristics (the test example of the present invention uses a uniform sampling method to select 25 points at equal intervals in the XOY plane). If non-uniform sampling is used, the distance between every two sampling points is different, which is suitable for use when the surface characteristics of the part to be measured are known and the flatness of a certain area needs to be accurately measured. For example: use a PLC control system to set two uniform sampling areas and an overall measurement area for rough measurement, and then set another area in the precise measurement area, which is a non-uniform sampling method.

[0082] It should be explained that a suitable fitting function is selected. Since the sampling points are discrete data, the fitting function is selected according to the needs. The fitting functions are: 1) fit (includes various types of models in Curve Fitting Toolbox, such as polynomial, plane, nonlinear, etc.); 2) regress (used for linear regression analysis, but only supports linear models, suitable for design matrices); 3) nlinfit (used for nonlinear regression fitting, suitable for custom complex nonlinear models); 4) fitlm (used for linear regression, suitable for more complex linear models, and can process classified data); 5) fitglm (used for fitting generalized linear models, suitable for classified data or more complex response variables); 6) mle (maximum likelihood estimation, can be used to fit binary models, suitable for custom statistical models); 7) lsqcurvefit (used for nonlinear least squares fitting, suitable for situations where custom nonlinear models are required); 8) fit (if the data points are in a grid, the fit function can be used for interpolation fitting); in the example of the present invention, interpolation method is selected for drawing. Commonly used interpolation methods include nearest neighbor interpolation, linear interpolation, polynomial interpolation, Lagrange interpolation, etc.

[0083] When making a rough assessment of the flatness of a plane, the nearest neighbor interpolation method can be used. That is, the distance between the interpolation points (X, Y) and (X1, Y1) can be calculated. The Euclidean distance formula can be used, that is, The known point u1 with the minimum distance is used as the coordinate of the interpolation point.

[0084] It needs to be explained that in order to be able to intuitively see the degree of inclination of the plane, another method can be used:

[0085] 1) Determine the interpolation area

[0086] First, determine the area formed by your data points. This area can be a rectangle, triangle, or other polygon.

[0087] 2) Create a grid

[0088] The area is divided into multiple small grid cells, such as rectangles or triangles. Linear interpolation is performed separately in each grid cell.

[0089] 3) Select the interpolation method

[0090] For rectangular meshes, bilinear interpolation is usually used (linear interpolation in both dimensions). For triangular meshes, linear interpolation within the triangle is used.

[0091] 4) Determine the query point location

[0092] Determine the locations in the grid of the query points you want to interpolate.

[0093] 5) Perform linear interpolation

[0094] For the grid cell where the query point is located, linear interpolation is performed using the linear interpolation method of the rectangular network.

[0095] Assume that the query point P(x, y) is located between the four vertices A(x0, y0), B(x1, y0), C(x1, y1), and D(x0, y1) of the rectangular grid. The interpolation u can be calculated by the following steps:

[0096] First, in the x direction, linear interpolation is performed using A and B to obtain ux.

[0097] Then, in the y direction, linear interpolation is performed using D and C to obtain uy.

[0098] Finally, combine dx and dy to obtain d=ux+(y-y0)×(uy-ux) / (y1-y0).

[0099] 6) Application results

[0100] Apply the calculated interpolation result to the position where interpolation is required.

[0101] It should be explained that the data points obtained in the experiment are used as the basis, and according to the data characteristics and requirements of the points, a suitable interpolation method is selected, such as linear interpolation, polynomial interpolation, etc.; the interpolation algorithm is written in matlab. Matlab has some built-in interpolation algorithms, such as interp1, interp2, interp3, etc., which can be used directly. For two-dimensional interpolation, interp2 is used. Its basic usage is u1=interp2(X, Y, d, X1, Y1, "method"), where X and Y are the coordinates of the sample points, V is the function value at the sample point, X1 and Y1 are the coordinates of the query point, and u1 is the interpolation result at the query point. The interp2 function supports a variety of interpolation algorithms, and the interpolation algorithm can be selected by method, such as "linear": bilinear interpolation algorithm; "nearest": nearest neighbor algorithm; "spline": cubic spline interpolation. Generate interpolation points using the selected interpolation method and algorithm; use the plot function to plot the original data points to visualize the experimental data distribution; on the same graph, use the plot function to plot the interpolation-generated points or interpolation curves.

[0102] In this optional embodiment, setting the coordinate origin and using the radio frequency identification ranging principle to quantify the transmission power includes the following steps:

[0103] S11, start the directional reader 6, configure the transmission power, transmission gain and working wavelength of the directional reader 6, and confirm the activation power of the radio frequency tag 7;

[0104] S12, setting the directional reader 6 and the radio frequency tag 7 at a preset reference distance, and using a power calculation formula to calculate the power received by the radio frequency tag 7 at the preset reference distance;

[0105] S13, move the directional reader / writer 6 to any point to be measured, measure the power received by the radio frequency tag 7, and calculate the actual distance between the directional reader / writer 6 and the radio frequency tag 7.

[0106] It should be explained that for the tag chip (i.e., the RFID tag 7), let its activation power be P w (When the input power is lower than the activation power, the tag chip will not work, that is, it will not return a signal to the reader) Suppose the transmission power of the reader antenna is P r , the transmission gain is G r , the tag antenna (i.e., RF tag) gain is G t , then the power received when the distance between the antenna and the tag is d is P t After sorting, we get:

[0107]

[0108] Where P t represents the power received by the RFID tag at the preset reference distance; τ represents the power transmission coefficient (i.e., the power transmission coefficient considering whether the impedance is matched); P r Indicates the transmission power of the directional reader; G r Represents the transmission gain of the directional reader; G t represents the RFID tag gain; l represents the distance between the RFID tag and the directional reader; A represents the parameter. Then, we only need to measure a reference distance l0 and the power P received at this distance. t0 The parameter A can be determined, and then the received power P can be obtained according to the power meter. t , the distance l at this time can be obtained.

[0109] In this optional embodiment, the power calculation formula is:

[0110]

[0111] Where P t represents the power received by the RFID tag at the preset reference distance; λ represents the working wavelength of the RFID tag; τ represents the power transmission coefficient (i.e., the power transmission coefficient considering whether the impedance is matched); P r Indicates the transmission power of the directional reader; G r Represents the transmission gain of the directional reader; G t represents the gain of the RFID tag; l represents the distance between the RFID tag and the directional reader.

[0112] In this optional embodiment, the formula for the vertical distance difference of the measuring points in plane geometry calculation is:

[0113]

[0114] In the formula, d represents the vertical distance difference; l0 represents the distance between two RFID tags; l1 and l2 both represent the distance between the directional reader and the RFID tag.

[0115] In summary, with the aid of the above technical solution of the present invention, the present invention is simple in design, easy to process and assemble, and can provide high-precision flatness measurement results through precise distance measurement and geometric calculation. It is more economical and affordable than traditional measuring equipment. The size and weight of the device for measuring plane flatness allow users to carry it easily, which is suitable for on-site measurement, and can achieve plane flatness measurement of large-area products, and is suitable for a variety of application scenarios. The present invention can be combined with a digital control system to achieve automatic sampling and data recording, and data processing and image drawing are performed through software such as Matlab, which is convenient for analysis and evaluation. The RFID technology and modern signal processing methods are used to improve the accuracy and reliability of the measurement. Due to the simple structure, it is easier to perform daily maintenance and calibration, which makes the present invention have potential application value in the field of industrial measurement, especially in situations where high-precision and portable measuring tools are required.

[0116] In the present invention, unless otherwise clearly stipulated and limited, the terms such as "installation", "setting", "connection", "fixation" and "screw-on" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral one; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be the internal connection of two elements or the interaction relationship between two elements. Unless otherwise clearly defined, ordinary technicians in this field can understand the specific meanings of the above terms in the present invention according to the specific circumstances.

[0117] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A device for measuring the flatness of a surface using RFID, comprising a horizontal slideway (1), characterized in that: A vertical slideway (2) is provided through a side wall at one end of the horizontal slideway (1); a reader / writer slide bar (3) is provided inside one side of the vertical slideway (2); a radio frequency identification slide bar (4) matched with the reader / writer slide bar (3) is provided inside the other side of the vertical slideway (2); and a movable component (5) is provided at the bottom of the radio frequency identification slide bar (4).

2. The device for measuring plane flatness using RFID according to claim 1, characterized in that: A directional reader / writer (6) is arranged on one side wall of the top of the reader / writer slide bar (3), and a radio frequency tag (7) is symmetrically arranged on one side wall of the top of the radio frequency identification slide bar (4).

3. The device for measuring plane flatness using RFID according to claim 2, characterized in that: Both end side walls of the vertical slideway (2) are symmetrically provided with slide grooves (8) that match the movable component (5).

4. The device for measuring plane flatness using RFID according to claim 3, characterized in that: A moving groove (9) matching with the vertical slideway (2) is provided on one side of the horizontal slideway (1).

5. The device for measuring plane flatness using RFID according to claim 4, characterized in that: The movable component (5) comprises fixed plates (501) symmetrically arranged on the side walls at both ends of the bottom of the radio frequency identification slide bar (4), a movable ball (502) is arranged between the bottoms of the two fixed plates (501), and a movable plate (503) is arranged on the side walls at one end of the top of the fixed plates (501).

6. The device and method for measuring plane flatness using RFID according to claim 5, characterized in that: The side walls at one end of the movable plate (503) are symmetrically provided with sliding columns (504) that match the sliding grooves (8).

7. A method for measuring the flatness of a surface using RFID, for implementing the measurement of the device for measuring the flatness of a surface using RFID as claimed in any one of claims 1 to 6, characterized in that: The method for measuring the flatness of a surface using RFID comprises the following steps: S1. Set the coordinate origin and use the radio frequency identification ranging principle to quantify the transmission power; S2, moving the RFID slider (4) to a measuring point on the plane to be measured, recording the plane coordinates of the measuring point at this time according to the moving distances in the horizontal and vertical directions, turning on the directional reader (6), obtaining the distance between the directional reader (6) and the two RFID tags (7), calculating the vertical distance difference of the measuring point according to the plane geometry, and recording the three-dimensional coordinate data of the measuring point; S3. Repeat step S2 to record the three-dimensional coordinate data of each measuring point. Record the three-dimensional coordinate data of all measuring points in a table and upload it to the analysis software. Generate a plane flatness image through data processing to intuitively display the flatness distribution.

8. The method for measuring plane flatness using RFID according to claim 7, characterized in that: The setting of the coordinate origin and the use of the radio frequency identification ranging principle to quantify the transmission power include the following steps: S11, starting the directional reader (6), configuring the transmission power, transmission gain and working wavelength of the directional reader (6), and confirming the activation power of the radio frequency tag (7); S12, setting the directional reader (6) and the radio frequency tag (7) at a preset reference distance, and using a power calculation formula to calculate the power received by the radio frequency tag (7) at the preset reference distance; S13, moving the directional reader / writer (6) to any point to be measured, measuring the power received by the radio frequency tag (7), and calculating the actual distance between the directional reader / writer (6) and the radio frequency tag (7).

9. The method for measuring plane flatness using RFID according to claim 8, characterized in that: The power calculation formula is: Where P t represents the power received by the RFID tag at the preset reference distance; λ represents the working wavelength of the RFID tag; τ represents the power transmission coefficient; P r Indicates the transmission power of the directional reader; G r Represents the transmission gain of the directional reader; G t represents the gain of the RFID tag; l represents the distance between the RFID tag and the directional reader.

10. The method for measuring plane flatness using RFID according to claim 9, characterized in that: The formula for the vertical distance difference of the measuring points in the plane geometry calculation is: In the formula, d represents the vertical distance difference; l0 represents the distance between two RFID tags; l1 and l2 both represent the distance between the directional reader and the RFID tag.

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